Methods for the prediction of a personalized esa-dose in the treatment of anemia

ABSTRACT

An integrative pharmacokinetic/pharmacodynamics (PK/PD) ESA-EpoR mathematical model calculates the binding behavior of erythropoiesis stimulating agents (ESA). The invention provides methods for the determining of ESA binding sites in cells or patients suffering from anemia. Knowing the amount of ESA binding sites enables the clinical practitioner to optimize the dosage regimen during a treatment of anemia, in particular in patients suffering from a cancerous disease. Further provided are methods for screening ESAs which have a higher specificity for cells strongly expressing the EPO receptor such as colony forming units-erythroid (CFU-E) cells, and not to cells with a low level of EPO receptor cell surface expression, which is the case in cancer cells. Also provided is a computer implemented method, comprising the use of the mathematical model of the invention.

RELATED APPLICATIONS

This Application is a Continuation of application Ser. No. 15/319,073,now U.S. Pat. No. 10,796,799, filed on Dec. 15, 2016, which is the U.S.National Stage of International Application PCT/EP15/63775, filed Jun.18, 2015, which designates the U.S., published in English, and claimspriority under 35 U.S.C. §§ 119 or 365(c) to European Application No.14173054.9, filed on Jun. 18, 2014 in the European Patent Office. Theentire teachings of the above applications are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention pertains to the use of an Integrativepharmacokinetic/pharmacodynamics (PK/PD) ESA-EpoR mathematical model forcalculating the binding behaviour of erythropoiesis stimulating agents(ESA). The invention provides methods for the determining of ESA bindingsites in cells or patients suffering from anemia. Knowing the amount ofESA binding sites enables the clinical practitioner to optimize thedosage regimen during a treatment of anemia, in particular in patientssuffering from a cancerous disease. Further provided are methods forscreening ESAs which have a higher specificity for cells stronglyexpressing the EPO receptor such as colony forming units-erythroid(CFU-E) cells, and not to cells with a low level of EPO receptor cellsurface expression, which is the case in cancer cells. Also provided isa computer implemented method, comprising the use of the mathematicalmodel of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A are plots showing depletion of Epo alfa and Epo beta by murineBaF3 cells stably expressing the murine EpoR (BaF3-mEpoR) whereasparental BaF3 cells had no impact underscoring the specificity of theassay.

FIG. 1B are plots of depletion by BaF3 cells stably expressing the humanEpoR (BaF3-hEpoR) or parental BaF3 cells.

FIG. 1C shows the K_(D) of the different ESA to the respectiveassociation and dissociation rates, revealing that the association ofNESP and CERA is much slower compared to Epo alpha and Epo beta whereasthe dissociation rate is enhanced.

FIG. 2A is a histogram of NSCLC cell lines H838, H1299, A549 and H1944,with H838 and H1299 indicating moderate expression levels of EpoR mRNAand A549 indicating low levels of EpoR mRNA.

FIG. 2B are gels indicating enrichment by immunoprecipitation anddetection by immunoblotting that reveals the presence of the EpoRprotein in H838 and H1299 cell lines and at very low levels in A549 cellline, whereas it was absent in H1944 cell line.

FIG. 2C are plots showing the binding properties of the EpoR expressedin the NSCLC cell lines H838, H1299, A549 and H1944, with Epo beta beingdepleted by the NSCLC cell lines harboring a functional EpoR, but not bythe EpoR negative NSCLC cell line H1944.

FIG. 3A is a plot of time-resolved analysis of Epo beta depletionrevealing rapid reduction of Epo beta from the supernatants of hCFU-Ebut not of hHSC that lack the EpoR.

FIG. 3B is a plot of hEpoR in H838 (H838-hEpoR) showing by enrichmentusing immunoprecipitation and immunoblotting that expression of EpoR washighly increased and the phosphorylated EpoR was substantially elevated.

FIG. 3C are gels of depletion experiments and model-based analysisrevealing binding properties rather similar to hCFU-E establishing theH838-hEpoR cell line as suitable model system to examine the impact ofdifferent ESA on cells harboring high levels of the EpoR as observed inthe hematopoietic system versus cells expressing low levels as in thetumor context.

FIG. 4A plot the results of stimulations that were performed fordifferent ESA concentrations and predicted the EC₅₀ for both Epo betaand CERA in cells with high EpoR levels.

FIG. 4B indicate that as cells deplete less Epo beta, Epo beta resultsin stronger activation than CERA in cells with low levels of EpoR.

FIG. 5A plots pharmacokinetic behavior of increasing CERA concentrationsin healthy volunteers, with circles showing the mean values of CERAconcentrations in serum, and solid lines representing the trajectoriespredicted for the CERA clearance for the given concentrations and theexperimental data.

FIG. 5B plotspharmacokinetic behavior of increasing CERA concentrationsin NSCLC patients in stage III or IV, with circles showing the meanvalues of CERA concentrations in serum, and solid lines representing thetrajectories predicted for the CERA clearance for the givenconcentrations and the experimental data.

FIG. 5C is a histogram indicating the number of CFU-E cells for eachcancer patient, shown as a relative comparison of CERA clearancecapability (% of CFU-E) of NSCLC patients and healthy subjects, andshowing a high patient-to-patient variability.

FIG. 6A shows an ESA-EpoR in vitro trafficking model.

FIG. 6B is an ESA-EpoR in vivo PK/PD model showing the correlationbetween the individual patient histories with the PK/PD data and theseones with the number of CFU-E per patients, and these ones with theoutcome of the ESA treatment.

FIG. 6C is an ESA-EpoR in vivo PK/PD model, including the additionalreactions of the production of Hb by active ESA-EPO-R signalling, andthe patient specific degradation of Hb.

FIG. 7 are plots of STAT5 phosphorylation in response to stimulationwith Epo beta or CERA in H838 and hCFU-E cells, indicating that theactivation of EpoR signaling by CERA is less effective in cells with lowlevels of the EpoR such as NSCLC cells (FIG. 7 left panel) compared tocells with higher levels of the EpoR like hCFU-E (FIG. 7 right panel).

FIG. 8A is an integrative PK/PD ESA-EpoR model that describes all NSCLCpatient data sets.

FIG. 8B is an integrative PK/PD ESA-EpoR model that describes a patientdata set involving NSCLC patient ID:2101 (clinical trial CSR NA17101).

FIG. 8C is an integrative PK/PD ESA-EpoR model that describes a patientdata set involving healthy subject ID:25 (clinical trial WP16422).

FIG. 8D is a histogram estimating the number of ESA-binding sites forindividual cancer patients, demonstrating that the distribution of theestimated KHb_deg parameter differs widely in healthy subjects and NSCLCpatients (FIG. 8D left panel), and showing a high patient-to-patientvariability and a very different distribution from the healthy subjects(FIG. 8D right panel).

FIG. 9A present the results of CERA treatment simulations based on thepatient-specific parameters in three NSCLC patients

FIG. 9B presents the results of an integrative PK/PD ESA-EpoRmathematical model that predicted a systematic overdosing of a largefraction of NSCLC IIIB-IV patients treated within the EMEA-recommendedESA guidelines for anemia in cancer.

FIG. 9C presents the results of an integrative PK/PD ESA-EpoRmathematical model that optimizes the ESA dosing and scheduling toachieve a hematological response within the limits of the ESAsguidelines for most of the NSCLC IIB-IV patients, minimizing the risk ofoverdosing.

FIG. 9D represent a prediction for all ESA regimens required toeffectively treat all the NSCLC IIIB-IV patients of the CSR NA17101clinical trial.

DESCRIPTION

Lung carcinoma is the most frequent cause of death in cancer with 1.59million of deaths in 2012, of which 80% were diagnosed as Non-Small CellLung Carcinoma (NSCLC). Most of the patients are diagnosed in a stageIIIB or IV and treated with a combination of platinum compounds andtaxanes, gemcitabine or vinorelbine as a first line of treatment. Inlung carcinoma there is a high prevalence of anemia ([Hb]≤11 g/dL),ranging from 50% to 70%, although in advanced stages it could reach upto 90%. The anemic grade depends on the therapy, tumor stage andduration of the disease. Cancer related anemia reduces the quality oflife (Cella et al, 2004) and it is considered a risk factor formortality in cancer patients (Caro 2001). Furthermore, it has beenreported that anemia affects the outcome of the anticancer therapy,diminishing the chemotherapy response in NSCLC patients (Albain 1991,MacRae 2002 and Robnett 2002).

The etiology of anemia in cancer is complex due to the multifactorialcauses such as deficiencies in vitamin B12 and folic acid, bleeding,haemolysis, inflammatory cytokines secreted in the tumor context andreduction in the iron uptake (Weiss and Goodnough N.Engl. J Med 2005)are some of the causal origins of cancer related anemia. In addition,platinum-based chemotherapy inhibits the renal production of Epo andexerts myelosuppresion what increases the anemia (Groopman 1999,Kosmidis 2005, Ludwig 2004).

Currently, there are two available therapeutic approaches for themanagement of anemia in cancer patients: homologous red blood cells(RBC) transfusions or administration of Erythropoiesis StimulatingAgents (ESAs). The first option has an immediate but transientimprovement of anemia. The disadvantages of the RBC transfusions are:the potential risk of infectious agent transmission, immunosuppression,hemolysis, allergic reactions, a non-sustained relief of anemia symptomsand the risk of transfusion-related acute lung injury (Klein 2007).Furthermore, the clinical demand of transfusions in lung carcinoma ishigher in NSCLC than in other cancers (Barret-Lee 2000), with 40%requiring at least one transfusion, and 22% requiring more than one(Langer 2002, Barret-Lee, Estrin 1999, Skillings 1999).

The second therapeutic alternative is based on the administration ofESAs. This approach increases and sustains the haemoglobin (Hb) levels,reduces the likelihood of RBC transfusions, and improves the quality oflife (Meta-analisis cochrane: Tonia, Melter, The Cochrane library 2012).ESA treatments increase the red blood cell (RBC) production by specificactivation of erythropoiesis receptor (EpoR) of erythrocytic progenitorsin the bone marrow (Egrie 1986, 2003) (Wu, Liu Lodish, Cell 1995).However, this treatment is not effective in 30% to 40% of patients. Thereasons underlying this failure are not yet defined, but different ESAadministration protocols showed a significant reduction of such a largeportion of patients (Hirsh 2007) suggesting the need of furtherprotocol-optimization in managing NSCLC related anemia. Anotherdisadvantage of the ESA treatments is that conflicting reports on theimprovement in tumor response and survival were published. The use ofESAs in cancer is restricted by label on the settings of only cancer andonly radiotherapy (Metanalisis Aapro 2012) (11 Meta-analyses 2010). Thisrestriction implemented by the national authorities was based on theoutcomes of the ENHANCE, DAHANCA-10, EPO-CAN-20 and AMG20010103 studies,in which found that ESA treatments increases cancer disease progression,thromboembolic events and mortality (Henke 2003 “ENHANCE”, Overgaard2007 “DAHANCA-10”, Wright et al. J Clin Oncol 2007 “EPO-CAN-20” andSmith et al 2008 “AMG 20010103”) (Metanalisis Aapro 2012).

Also reported was an increment of mortality in the ESA treated patientsin the chemotherapy setting (Leyland-Jones 2005 “BEST”), (Hedenus 2003“AMG 20000161”), (Thomas 2008) and “PREPARE” (Untch 2011a, 2011b),(IV:Katodritou 2008) (Bennett 2008, Glaspy 2010), but several studiescontradicted the previous results reporting no significant difference inmortality (Pirker et al 2008), (Moebus 2010) (Engert 2010), norsignificant impact on the disease progression (Warner 2004, Reed 2005,Bohlius 2009, Gupta 2009, Ludwig 2009, Nagel 2011, Hershman 2009, Nitz2011, Machtay 2007 and Glaspy et al 2010). There are also other studiesthat reported an increment of therapy effect by ESA treatment (Hadland2009), and an increment of survival benefit as well (Littlewood 2001,Vansteenkiste 2002, and Delarue 2013).

These contradicting reports aimed to perform meta-analyses of thedifferent trials. All meta-analyses reported that ESAs treatments reducethe transfusions requirements but still there are some contradictingfindings regarding the mortality risk of ESA treatments in chemotherapysettings. (Bennett 2009, Bohlius 2009, Tonelli 2009, Hedenus 2005,Boogaerts 2006, Seidenfeld 2006, Ludwig 2009, Aapro 2009b, Glaspy 2010,Tonia et al Cochrane 2012). The reasons for such variability ofconclusions might be due to differences in the study designs,heterogeneity of the treated patients, the varying ESA dose regimens anddata analysis.

Since the first safety issues about ESA treatments were reported in2003, several groups worked in the hypothesis of a functional EpoR intumor context, as the logical mechanism exerting the tumor progressionunder ESA treatments in anemic cancer patients. In tumor tissue andcarcinoma cell lines, EpoR mRNA expression levels were detected but verylow in comparison with erythroid progenitors. The results werereproduced at protein level by western blot, immunohistochemistry, andin an animal model. These findings were however questioned by othergroups due to the use of unspecific antibodies in some of the studies,the lack of signaling activation upon ESA stimulation, absence of EpoRin biopsies or the non-effect of ESAs treatment in tumor animal models.In the positive cases for specific EpoR expression at transcript andprotein levels, EpoR levels were ranging from 10- up to 1000-fold lowerthan in Epo responsive cell lines, or by overexpression of receptor orin erythroid progenitors. This low level of EpoR expression innon-erythroid cells is an intrinsic liability of any experimentalapproach to study on EpoR presence and functionality upon ESAstimulations in tumor cells. Furthermore, the radioactive Epo-bindingassay is one of the most sensitive approaches at the time of revealingESA and EpoR binding behavior on the cellular surface. It has beenreported that lower levels than 50 receptors per cell makes themeasurements unreliable (Um 2007). The very low expression of EpoR inthe tumor cell lines and tissue in addition to wide used of unspecificantibodies have constituted so far the “Achilles heel” of the functionalstudies of EpoR in a tumor context.

The characterization and prediction of an effective and safer ESAtreatment of anemia in cancer and chemotherapy setting constitutes acomplex question. The outcome is influenced by the dynamic interplay ofmany components, and it has to be addressed from multiple angles, whichrequires quantitative experimental studies at different levels. Thesedifferent perspectives go from molecular studies of EpoR activation in asingle cell to the study of ESAs pharmacokinetic (PK) andpharmacodynamics (PD) in carcinoma patients. Due to the complexity,non-linear relationship and involvement of multiple scales, thisrequires a Systems Biology approach that combines experimental datageneration and mathematical modeling. The inventors focused in NSCLC,due to its high impact in the populations and the high prevalence ofanemia. This would also simplify the heterogeneity of the outcomes inthe ESA treatments and avoid any effect by the different underlyingmalignancies (11:24,32). Due to the wide variation of responses to ESAtreatments in NSCLC patients, the inventors used individual patientdata, in order to standardize and harmonize outcomes across the clinicaltrial. This approach will allow us to identify and correlate definedpatient populations with hematological responses. The inventors alsoperformed model-based predictions of the minimal personal effective ESAconcentration (MPEC) in order to avoid the transient overdosing, whichis suspected to be associated with thrombovascular events and potentialEpoR activation in tumor context.

Mathematical modeling of biological systems has become a widely usedapproach to better understand the system behavior as a whole rather thanobserving isolated parts (Kitano, 2002). The rapid development ofquantitative molecular biology (Cox and Mann, 2011) enables to calibratemathematical models to experimental data and therefore to generate modelpredictions. Established approaches for modeling and parameterestimation are publicly available in software tools like SBML-PET,COPASI or PottersWheel (Zi and Klipp, 2006; Hoops et al., 2006; Maiwaldand Timmer, 2008).

In view of the unsolved questions regarding the use of ESA in thetreatment of anemia, in particular in the context of a cancer patient,it was an objective of the present invention to provide novel means andmethods to assess the optimal dosage of ESA in a patient and thereby toavoid over- or under dosing. Furthermore the invention intends toprovide diagnostic tools to supply the clinical practitioner withadditional information about the anaemic status of a patient beforepreparing a treatment plan.

In one aspect the above problem is solved by a method for determiningthe dosage of an Erythropoiesis Stimulating Agent (ESA) that issufficient for treating anemia in a patient, the method comprising thesteps of (a) Calculating from the hemoglobin concentration of thepatient from at least two separate time points the patient's individualhemoglobin degradation rate (degradation of hemoglobin per time), (b)Determining the concentration of hemoglobin from a recent blood sampleobtained from the patient (the patient's present hemoglobinconcentration), and (c) Calculating based on the patient's hemoglobindegradation rate and the patient's present hemoglobin concentration theESA dosage sufficient for treating the anemia in the patient. The methodis preferably performed in-vitro.

The step of calculating the ESA dosage is preferably performed using thenon-linear dynamic pharmacokinetic (PK) hemoglobin (Hb) ESA-EPO-Rpathway model as described in detail herein below.

In context of the herein described invention the hemoglobinconcentration of the patient (or subject, terms which are used herein assynonyms) is preferably determined through blood samples taken from thepatient. Methods for calculating the haemoglobin concentrations are wellknown in the art. Alternatively, since most anemia patients have atreatment history where haemoglobin concentrations were determined atmultiple time points, the patients hemoglobin degradation rate may becalculated from these values taken from the individual patient's medicalfile.

Another aspect of the invention pertains to an ESA for use in thetreatment of anemia of a patient, wherein the treatment comprises,

-   -   (a) Calculating an ESA dosage according to a method of any of        claims 1 to 3,    -   (b) Administering to the patient an ESA dosage as calculated in        (a),    -   (c) Optionally, monitoring the patient's hemoglobin        concentration over time after the administration in (b),    -   (d) Optionally, repeating step (a) and (d).

The administration is preferably a subcutaneous injection.

The above problem is solved in a further aspect by an ErythropoiesisStimulating Agent (ESA) for use in the personalized treatment of anemia,the treatment comprising the steps of

-   -   (a) Administration of a (preferably clinically safe) dose of an        ESA to an individual patient suffering from anemia,    -   (b) Monitoring the clearance of said ESA from the serum in said        patient,    -   (c) Calculating from the clearance of said ESA in said patient        the number of initial ESA binding sites present in said patient        using a non-linear dynamic pharmacokinetic (PK) ESA-EPO-R        pathway model, and    -   (d) Adjusting the individual dosage of said ESA for said        treatment in accordance with the number of ESA binding sites        calculated in (c),    -   (e) Optionally, repeating steps (b) to (d).

In an alternative aspect, the invention may relate to an ErythropoiesisStimulating Agent (ESA) for use in the personalized treatment of anemia,the treatment comprising the steps of

-   -   (a) Administration of a (preferably clinically safe dose) of an        ESA to an individual patient suffering from anemia and        determining the level of Hb at the time the ESA is administered,    -   (b) Monitoring the concentration of Hb in said patient,    -   (c) Calculating from change of concentration of Hb in said        patient the number of initial ESA binding sites present in said        patient using a non-linear dynamic pharmacokinetic (PK)        hemoglobin (Hb) ESA-EPO-R pathway model, and    -   (d) Adjusting the individual dosage of said ESA for said        treatment in accordance with the number of ESA binding sites        calculated in (c),    -   (e) Optionally, repeating steps (b) to (d).

As an alternative embodiment the individual dosage of said ESA iscalculated on the basis of the patient's hemoglobin degradation rate.Surprisingly it could be shown in context of the present invention thateach patient has a specific hemoglobin degradation rate which correlateswith the clinical development of anemia in the patient. Therefore thepresent invention discloses an ESA for the treatment of anemia in apatient wherein the ESA dosage using the herein described non-lineardynamic pharmacokinetic (PK) hemoglobin (Hb) ESAEPO-R pathway model onbasis of a predetermined hemoglobin degradation rate, the specificbiding properties of the used ESA in the treatment (for example the EC₅₀of EPOR occupancy by the ESA) and the present hemoglobin concentrationat the time the treatment is started. Hence an embodiment pertains to anESA for use in the treatment of anemia in a patient, wherein thetreatment comprises the initial determination of the patient'shemoglobin degradation rate.

The hemoglobin degradation rate may either be determined by measuringhemoglobin concentrations in the patient at several time points, forexample in an ESA naïve or ESA receiving patient, or using the patient'sprevious treatment history. In accordance with the herein describedmathematical model the specific characteristics of the ESA to be used intherapy, for example CERA, are used for determining the ESA dosage.

Based in the initial experiments in vitro (ESA depletion experiments) asdescribed in the example section, the mathematical model as discloseddescribes the binding properties of each ESA: the association rate“k_(on)” and the dissociation rate “k_(off)” (the dissociation constant“K_(D)” is defined as koff/kon). Based in the binding properties of eachESA, the herein disclosed model can calculate the integral occupancy ofthe EpoR on human CFU-E for 60 minutes. The EC₅₀ (ESA concentrationrequired to obtain half-maximum EpoR occupancy) is calculated for eachESA and this correlates with the ESA activity in hCFU-E. In theintegrative non-linear dynamic pharmacokinetic (PK) hemoglobin (Hb)ESA-EPO-R pathway model, the integral occupancy of the ESA-EpoR islinked to Hb production. The amount of ESA-EpoR is, among all the otherparameters, depending on the k_(on) and the k_(off) rate of the specificESA. Based on the ESA depletion experiments, the mathematical modelcalculates k_(on) and k_(off) for each ESA. This data can be used (i) tocalculate EC₅₀ values for each ESA and (ii) calculate Hb values based onESA injections. Thereby, the using the non-linear dynamicpharmacokinetic (PK) hemoglobin (Hb) ESA-EPO-R pathway model of theinvention, the ESA dosage for achieving a production of hemoglobin inthe anemia patient that is sufficient to alleviate the anemia can becalculated.

The term “anemia” in context of the herein described invention shallrefer to a condition wherein the red blood cells are reduced. Anemia istypically diagnosed on a complete blood count. Apart from reporting thenumber of red blood cells and the hemoglobin level, the automaticcounters also measure the size of the red blood cells by flow cytometry,which is an important tool in distinguishing between the causes ofanemia. Examination of a stained blood smear using a microscope can alsobe helpful, and it is sometimes a necessity in regions of the worldwhere automated analysis is less accessible. In modern counters, fourparameters (RBC count, hemoglobin concentration, MCV and RDW) aremeasured, allowing others (hematocrit, MCH and MCHC) to be calculated,and compared to values adjusted for age and sex. Some counters estimatehematocrit from direct measurements. In the context of the presentinvention anemia is present if an individual has a hemoglobin (Hb)concentration of less than 14 g/dL, more preferably of less than 12g/dL, most preferably of less than 11 g/dL.

In certain embodiments of the invention the anemia to be treated inaccordance with the described methods is an anemia that has developedaccording to any possible cause or disease. This includes all types ofcancer, all inflammation-associated anemia (chronic infection disease,autoimmune or rheumatologic disorders and any other illnesses ortreatments that results in anemia based on reduced endogenous Epoproduction, inefficient eryhtropoiesis or increased desruction of redblood cells). Furthermore, and particularly preferred, is that theanemia is caused by chronic kidney disease (CKD), myelodysplasticsyndrome (MDS), or is anemia associated to myelofibrosis, anemia incontext of HIV, aplastic anemias, anemia in premature infants,non-severe aplastic anemia, anemia in beta thalassemia, anemia in sicklecell disease and ESA erythropoiesis stimulation after allogeneichematopoietic stem cell transplantation.

The inventors of the present invention surprisingly discovered that amathematical model describing the EPO-EPO-R signaling pathway in a cellcan be adapted to predict the behavior of not only ESAs in a cell, butalso of the dynamics of ESAs administered to a patient.

Initially the model is able to describe at cellular level the activityof the different ESAs based in the affinity of each ESA (time of EpoRoccupancy). This activity corresponds to the EPO-R activation by ESAbinding to the EPO receptor. This activation of the EPO-R will inducethe proliferation and maturation of the erythropogenitors, the maincellular population on the body that express EpoR into erythrocytes. Forthe present invention the initial core model that describes the EpoRactivation at cellular level by ESA was extended in order to be used ina physiological situation in an organism, in particular a human patient.Clearance of an administered ESA in the blood compartment, transport ofan subcutaneous administered ESA into the blood compartment andsaturable clearance of the ESA in the interstitial compartment wereadded to the initial model. This extended version of the initialESA-EPO-R model was surprisingly able to describe the publishedpharmacokinetic (PK) and pharmacodynamics (PD) experimental data of eachESA as shown in the examples. The inventors could characterize inducedanemia by cancer and chemotherapy in individual patients at colonyforming unit of erythroids (CFU-E), the progenitors of the erythroids.It was observed that patients in the same cancer type and disease stage(FIG. 5c ) show different numbers of CFU-E. This explains the differentESA treatment outcomes observed in patients−40% of the NSCLC patients donot respond to ESA treatment in the current approved posology (protocolto treat anemic patients with cancer). Lower levels of CFU-E means lowerlevels of response to ESA treatments and it correlated with theindividual outcomes at hemoglobin levels (Hb).

In the context of the invention which is described in the following, themathematical models are all based on the basic findings as published andpublically accessible in the publication Becker V et al., Science. 2010Jun. 11; 328(5984):1404-8. This reference is incorporated in itsentirety, for the purpose of understanding the application of themathematical models in the present invention. The models used in contextof the present invention were adjusted to answer the respectivequestions of the herein disclosed invention. In this respect the term“non-linear dynamic EPO-EPO-R pathway model” shall refer to the model aspublished by the above Becker V et al. 2010 reference. The term“non-linear dynamic ESA-EPO-R pathway model” shall refer to an newversion of the non-linear dynamic EPO-EPO-R pathway model, whichdescribes the binding/dissociation dynamics of ESAs to the EPO-R on acellular level. The term “non-linear dynamic pharmacokinetic ESA-EPO-Rpathway model” shall refer to the non-linear dynamic ESA-EPO-R pathwaymodel which is adjusted to the situation in an organism, in particular ahuman patient. The basic rationales for the models disclosed herein areprovided in the Materials and Methods section of the presentapplication. Thus itis a preferred embodiment that the non-lineardynamic pharmacokinetic (PK) ESAEPO-R pathway model considers clearanceof the administered ESA in the blood compartment, transport of theadministered ESA from the interstitial compartment into the bloodcompartment, and clearance of the ESA in the interstitial compartment.

The basic application of the mathematical methods as required by theherein described inventive methods is standard to the person of skill inthe field of systems biology. Using the information as provided by thepresent patent application, the person of skill in view also of theBecker V et al. 2010 publication can perform the necessary steps to workthe invention.

For the present disclosure the following variables, constants andacronyms are used:

TABLE 1 Acronyms CFU-E Colony forming unit-erythroid NSCLC Non-smallcell lung carcinoma Hb Hemoglobin RBC Red blood cells Epo ErythropoietinEpoR Erythropoietin receptor PK Pharmacokinetics PD PharmacodynamicsMEPC Minimal Personal Effective ESA Concentration CKD Chronic kidneydisease MDS Myelodysplastic syndrome NESP Novel erythropoiesisstimulating protein CERA Continuous erythropoietin receptor activatorSTAT5 Signal transducer and activator of transcription 5 EC50Half-maximal effective concentrations ODE Ordinary differential equationU Units

TABLE 2 Variables ESA Erythropoiesis-stimulating agent in medium / bloodEpo Erythropoietin EpoR Erythropoietin receptor ESAEpoR Complex of ESAbound to EpoR on the cell surface ESAEpoR_(i) Internalized complex ofESA bound to EpoR dESA_(i) Intracellular degraded ESA dESA_(e)Extracelullar degraded ESA ESA_(sc) ESA in the subcutaneous compartmentHb Hemoglobin in blood

TABLE 3 Kinetic constants k_(sc)_clear ESA clearance constant in thesubcutaneous compartment k_(sc)_clear_sat Saturation of ESA clearance insubcutaneous compartment k_(sc)_out ESA transportation constant to theblood compartment k_(clear) ESA clearance constant in the bloodcompartment k_(on) ESA-EpoR association rate/on-rate k_(off) ESA-EpoRdissociation rate/off-rate K_(D) ESA-EpoR dissociation constant(k_(off)/k_(on)) k_(t) Ligand-independent receptor turnover rate B_(max)Number of ESA binding sites per cell/per patient k_(e) ESA-EpoR complexinternalization constant k_(ex) ESA and EpoR recycling constant k_(di)Intracellular ESA degradation constant k_(de) Extracellular ESAdegradation constant k_(Hb)_pro Hemoglobin production constant by theESA-EpoR complex K_(Hb)_deg Hemoglobin degradation constant (net loss ofhemoglobin)

The models disclosed in the present application are based on thefollowing ordinary differential equations with reference to FIG. 6. Thismodel describes the following reaction scheme which is based on priorbiological knowledge. The ESA binds reversibly (k_(on) respectivelyk_(off)) to the Epo receptor (EPO-R) which is exposed on the cellsurface. Thereby, the ESA-receptor complex gets activated and can inducephosphorylation of downstream signaling molecules like STAT5. TheESA-receptor complex is then internalized (k_(e)) into intracellularreceptor pools where ESA is either exported (k_(ex)) or degraded (k_(de)and k_(di)) and the receptor can translocate back to the membrane(k_(ex)). In addition, a ligand independent turnover (k_(t)) of EpoRensures that the cell is sensitive for a broad range of ligandconcentrations. In the equations [ ] denote concentrations of therespective components. These are, EpoR or EPO-R is the EPO receptor,ESAEpoR is the complex of ESA bound to the EPO-R. ESAEpoR_(i) is theinternalized complex. dESA is degraded ESA, either cell-internally(dESAi) or extracellular (dESAe). The equations are:

$\begin{matrix}{\frac{d\lbrack{ESA}\rbrack}{dt} = {{{- k_{on}} \cdot \lbrack{ESA}\rbrack \cdot \lbrack{EpoR}\rbrack} + {k_{off} \cdot \lbrack{ESAEpoR}\rbrack} + {k_{ex} \cdot \lbrack{ESAEpoRi}\rbrack}}} & (1.1) \\{\frac{d\lbrack{EpoR}\rbrack}{dt} = {{{- k_{on}} \cdot \lbrack{ESA}\rbrack \cdot \lbrack{EpoR}\rbrack} + {k_{off} \cdot \lbrack{ESAEpoR}\rbrack} + {k_{t} \cdot B_{\max}} - {k_{t} \cdot \lbrack{EpoR}\rbrack} + {k_{ex} \cdot \lbrack{ESAEpoRi}\rbrack}}} & (1.2) \\{\frac{d\lbrack{ESAEpoR}\rbrack}{dt} = {{k_{on} \cdot \lbrack{ESA}\rbrack \cdot \lbrack{EpoR}\rbrack} - {k_{off} \cdot \lbrack{ESAEpoR}\rbrack} - {k_{e} \cdot \lbrack{ESAEpoR}\rbrack}}} & (1.3) \\{\frac{d\lbrack{ESAEpoRi}\rbrack}{dt} = {{k_{e} \cdot \lbrack{ESAEpoR}\rbrack} - {k_{ex} \cdot \lbrack{ESAEpoRi}\rbrack} - {k_{di} \cdot \lbrack{ESAEpoRi}\rbrack} - {k_{de} \cdot \lbrack{ESAEpoRi}\rbrack}}} & (1.4) \\{\frac{d\lbrack{dESAi}\rbrack}{dt} = {k_{di} \cdot \lbrack{ESAEpoRi}\rbrack}} & (1.5) \\{\frac{d\lbrack{dESAe}\rbrack}{dt} = {k_{de} \cdot {\lbrack{ESAEpoRi}\rbrack.}}} & (1.6)\end{matrix}$

For the model simulating the in-vivo patient situation this model isextended resulting in system of seven coupled ordinary differentialequations (ODE). The expanded model in figure (6b) describes thesituation including the blood and interstitium compartments. IntravenousESA is either cleared in the blood compartment (k_(clear)) or binds tothe EPO-R (k_(on), k_(off)). Subcutaneous applied ESA (ESA_(SC)) istransported to the blood compartment (k_(sc_out)) or saturable clearedin the interstitial compartment (k_(sc_clear_sat)). The non-lineardynamic pharmacokinetic ESA-EPO-R pathway model:

$\begin{matrix}{\frac{d\left\lbrack {ESA}_{SC} \right\rbrack}{dt} = {{{- k_{sc\_ clear}} \cdot \frac{\left\lbrack {ESA}_{SC} \right\rbrack}{\left( {k_{{sc\_ clear}{\_ sat}} + \left\lbrack {ESA}_{SC} \right\rbrack} \right)}} - {k_{{sc\_ ou}t} \cdot \left\lbrack {ESA}_{SC} \right\rbrack}}} & \left( {2.1.} \right) \\{\frac{d\lbrack{ESA}\rbrack}{dt} = {{k_{{sc}_{out}} \cdot \left\lbrack {ESA}_{SC} \right\rbrack} - {k_{clear} \cdot \lbrack{ESA}\rbrack} - {k_{on} \cdot \lbrack{ESA}\rbrack \cdot \lbrack{EpoR}\rbrack} + {k_{off} \cdot \lbrack{ESAEpoR}\rbrack} + {k_{ex} \cdot \lbrack{ESAEpoRi}\rbrack}}} & \left( {2.2.} \right) \\{\frac{d\lbrack{EpoR}\rbrack}{dt} = {{{- k_{on}} \cdot \lbrack{ESA}\rbrack \cdot \lbrack{EpoR}\rbrack} + {k_{off} \cdot \lbrack{ESAEpoR}\rbrack} + {k_{t} \cdot B_{\max}} - {k_{t} \cdot \lbrack{EpoR}\rbrack} + {k_{ex} \cdot \lbrack{ESAEpoRi}\rbrack}}} & \left( {2.3.} \right) \\{\frac{d\lbrack{ESAEpoR}\rbrack}{dt} = {{k_{on} \cdot \lbrack{ESA}\rbrack \cdot \lbrack{EpoR}\rbrack} - {k_{off} \cdot \lbrack{ESAEpoR}\rbrack} - {k_{e} \cdot \lbrack{ESAEpoR}\rbrack}}} & \left( {2.4.} \right) \\{\frac{d\lbrack{ESAEpoRi}\rbrack}{dt} = {{k_{e} \cdot \lbrack{ESAEpoR}\rbrack} - {k_{ex} \cdot \lbrack{ESAEpoRi}\rbrack} - {k_{di} \cdot \lbrack{ESAEpoRi}\rbrack} - {k_{de} \cdot \lbrack{ESAEpoRi}\rbrack}}} & \left( {2.5.} \right) \\{\frac{d\lbrack{dESAi}\rbrack}{dt} = {k_{di} \cdot \lbrack{ESAEpoRi}\rbrack}} & \left( {2.6.} \right) \\{\frac{d\lbrack{dESAe}\rbrack}{dt} = {k_{de} \cdot {\lbrack{ESAEpoRi}\rbrack.}}} & \left( {2.7.} \right)\end{matrix}$

Since the amount of hemoglobin (Hb) in a patients serum is directlycorrelated to the activity of ESA-EPO-R system, the invention mayinstead of determining the concentration of the ESA after initialadministration of the ESA as a function of time, determine the Hbconcentration, which is a standard parameter observed during anemiatreatment. In this embodiment, the above model comprises the additionalreactions of the production of Hb by the activated ESA-EPO-R(k_(Hb_pro)) and the patient specific degradation of Hb (k_(Hb_deg)).

In this case the model includes the additional ODE:

$\begin{matrix}{{\frac{d\left\lbrack {Hb} \right\rbrack}{dL} = {{k_{Hb_{pro}} \cdot \lbrack{ESAEpoR}\rbrack} - {k_{Hb_{\deg}} \cdot \lbrack{Hb}\rbrack}}}\;} & \left( {2.8.} \right)\end{matrix}$

For both models the dissociation constant of K_(D) is defined as

K _(D) =k _(off) /k _(on)  (3.1)

In these models B_(max) is the initial number of binding sites for ESA.

Further explanation of the equations is provided in the example sectionand FIG. 6.

The values for the respective concentrations of elements and the allconstants used in the above equations can be determined experimentallyusing, for example, a method known to the skilled person or the methodsprovided herein below in the example section.

The object of the present invention is solved in an additional aspect byan Erythropoiesis Stimulating Agent (ESA) for use in a method ofdiagnosing the anemic status in a patient, the method comprising thesteps of

-   -   (a) Administering to said patient a clinically safe dosis of an        ESA,    -   (b) Assessing the clearance of the administered ESA in the serum        of said patient over time,    -   (c) Calculating from the clearance of said ESA using a        non-linear dynamic pharmacokinetic (PK) ESA-EPO-R pathway model        the amount of ESA binding sites in said patient, which is        predictive for the anemic status of the patient.

In accordance with the present invention, a clinically safe dose of anESA is a dose approved by the authorities for the treatment of anemia.

In the herein described methods clearance rate of an ESA in the serum ofa patient is determined. Preferably, and this holds true for all aspectsand embodiments as described herein, the clearance rate (or change ofconcentration) of said ESA is determined based on the initial dose ofESA administered to a patient. Subsequent to the initial ESAadministration, samples obtained from a patient can be analyzed for theremaining ESA concentration for at least one time point subsequent tothe initial ESA treatment. Ideally, the ESA concentration is observedover several time points, for example 1 to 6 weeks, preferably 1 to 3weeks, and includes at least 2, preferably 5, more preferably 7 to 10independent measurements of ESA concentration at different time points.An example for an observation plan would be the administration of theESA at day 0, and the subsequent measuring of the ESA concentration inthe patient at days 1, 2, 3, 5, 7, 10 and 14. This may be adjusteddepending on the clinical scenario. For the alternative embodiment ofthe invention regarding the calculation of initial ESA binding sitesbased on the observation of the change of Hb concentration in a patient,the same principle is applied.

In a certain embodiment of the invention the ESA is any ESA known to theskilled person, which includes in particular EPO biosimilars, but ispreferably selected from the group of Epoetin alfa, Epoetin beta, Novelerythropoiesis stimulating protein (NESP) and Continuous erythropoietinreceptor activator (CERA). CERA is preferred for the herein describedinvention.

The problem of the invention is also solved by a method for monitoringanemia in a patient who received at an earlier time point a dose of anESA, comprising the steps of

-   -   (a) Providing a serum sample from a patient suffering from        anemia who received at an earlier time point a dose of an ESA,    -   (b) Measuring the concentration of hemoglobin in said sample,    -   (c) Calculating the amount of ESA binding sites based on the        hemoglobin concentration in said sample using a non-linear        dynamic pharmacokinetic (PK) ESA-EPO-R pathway model,        wherein the amount of ESA binding sites indicates the anemic        status of a patient.

Preferable the calculation is further based on the initial ESA dose, andthe initial Hb concentration in the patient at the time the ESA wasadministered.

In context of the here described invention a patient is preferably apatient that is suffering from anemia in the context of a cancerdisease, the cancer disease preferably being a lung cancer such asnon-small cell lung cancer (NSCLC).

In preferred embodiments the non-linear dynamic pharmacokinetic (PK)ESA-EPO-R pathway model is based on a system of the ordinarydifferential equations (ODE) as described above. In this context theinvention seeks to obtain the initial number of ESA binding sites, whichis B_(max). B_(max) is therefore predictive for or an approximation ofthe colony forming unitserythroid (CFU-E).

Another aspect of the invention pertains to a method for identifying anErythropoiesis Stimulating Agent (ESA) having a specific activity forcells with a high cell surface expression of Erythropoietin-receptor(EPO-R), comprising the steps of

-   -   (a) Obtaining the half maximal effective concentrations (EC50)        of a candidate ESA and a reference ESA for EPO-R activation in a        first cell,    -   (b) Obtaining the EPO-R activation induced by the candidate ESA        and the reference ESA at their respective EC50 as obtained        in (a) in a second cell, wherein said second cell is        characterized by a significantly lower cell surface expression        of EPO-R compared to the first cell,        wherein a decreased activation of EPO-R in said second cell by        the candidate ESA compared to the activation of EPO-R in said        second cell by the reference ESA, is indicative for the        specificity of said candidate ESA for cells with a strong cell        surface expression of EPO-R.

The above method may be performed solely in-silico or in-vitro.Preferably Epoetin alfa or beta are selected as reference ESA. Howeveralso other ESA which have similar characteristics, which can be derivedfrom performing the inventive method, can be used as reference ESA.

Preferred is however that the method is an in-silico method and thatsaid EPO-R activation is calculated with a non-linear dynamic ESA-EPO-Rpathway model, more preferably according to the equations as describedabove. The EPO-R activation is preferable the integral of ESA bound tothe EPO receptor ([ESAEPO-R]), for example for the first 60 minutesafter stimulation. The time frame is however not essential to obtain theactivation of the EPO signaling.

Preferably the calculation of the EPO-R activation in context of theabove in-silico method comprises the input or the obtaining of thedissociation constant KD for at least the candidate ESA, and predictingthe EPO-R activation over a period of time according to a non-lineardynamic ESA-EPO-R pathway model.

The ESA identified by the method is specific for cells expressing highamount of cell surface EPO-R and therefore, this ESA is characterized bybeing specific for colony forming unit-erythroid (CFU-E) cells. Cellshaving a low cell surface expression of EPO-R are in context of thepresent invention tumor cells, such as lung cancer tumor cells, inparticular non-small cell lung cancer cells.

For performing the method in-vitro, it may be preferred that said firstcell is a cell ectopically expressing EPO-R, such as H838-EpoR, and/orwherein said second cell is not ectopically expressing EPO-R, such asH838.

The problem of the invention is additionally solved by a computerimplemented method for predicting or assessing the number of colonyforming units-erythroid (CFU-E) or an approximation thereof, in apatient, wherein the patient has received an administration of an ESA atan earlier first point of time, the method comprising the steps of:

-   -   (a) Obtaining the initial administered ESA dose,    -   (b) Obtaining the concentration of said ESA in a serum sample of        said patient at at least one second time point after the initial        administration of said ESA to said patient.    -   (c) Determining the concentration rate of said ESA as a function        of time in said patient    -   (d) Calculating based on a non-linear pharmacokinetic (PK)        ESA-EPO-R model and the concentration rate of said ESA in said        patient the initial number of ESA binding sites in said patient,        wherein the initial number of ESA binding sites in said patient        is predictive for the number of CFU-E in said patient.

An alternative aspect provides a computer implemented method forpredicting or assessing the number of colony forming unit-erythroid(CFU-E) or an approximation thereof, in a patient, wherein the patienthas received an administration of an ESA at an earlier first point oftime, the method comprising the steps of:

-   -   (a) Obtaining the hemoglobin (Hb) concentration in said patient        at the time point of the initial ESA administration,    -   (b) Obtaining the concentration of Hb in said patient at at        least one second time point after the initial administration of        said ESA to said patient.    -   (c) Determining the change in Hb in said patient as a function        of time,    -   (d) Calculating based on the change of Hb in said patient using        a non-linear pharmacokinetic (PK) ESA-EPO-R model the initial        number of ESA binding sites in said patient,        wherein the initial number of ESA binding sites in said patient        is predictive for the number of CFU-E in said patient.

Another aspect of the invention then relates to a computer implementedmethod for predicting the amount of initial ESA binding sites in apatient, the method comprising the steps of: obtaining the clearancerate of an ESA after initial administration of said ESA to a patient asa function of serum concentration of the ESA of time, calculating basedon a non-linear pathway model the number of initial ESA binding sites(Bmax). Preferably the non-linear pathway model is a non-linear dynamicPK ESA-EPO-R pathway model.

The computer implemented method for assessing the number of ESA bindingsites in a cell, or a an organism, may alternatively comprise the stepsof

-   -   (a) In vitro determination of the clearance rate of an ESA in        said cell or organism at at least one time point subsequent to        the addition/administration of an initial ESA dose to said cell        or organism,    -   (b) Calculating the amount of ESA binding sites in said cell or        organism based on the clearance rate of the ESA using a        non-linear dynamic EPO-R pathway model.

However, preferred is the above method wherein said organism is apatient, preferably a human patient, or wherein said cell is a cellendogenously expressing the EPO-R receptor, such as a red blood cellprecursor cell, or a tumor cell.

Preferably said organism is a human patient. In this scenario step (a)constitutes the in vitro determination of the clearance rate of an ESAin a serum sample of a patient at a time point subsequent to theadministration of an initial ESA dose to said patient, and step (b)constitutes calculating the amount of ESA binding sites based on theclearance rate of the ESA using a non-linear dynamic EPO-R pathwaymodel.

In a preferred embodiment of the invention the computer implementedmethod requires for the calculating step (b) as input the clearance rateof an ESA in said cell or organism as a function of ESA concentrationover time as determined in (a), and a dissociation constant K_(D) thatis specific for the ESA added/administered to said cell or organism.

Yet another aspect of the invention provides a computer-readable storagemedium having computer-executable instructions stored, that, whenexecuted, cause a computer to perform a computer implemented methodaccording to the present invention.

In preferred embodiments of all aspects of the invention the K_(D) ofthe ESA is about 16 pM for Epoetin alfa, about 17 pM for Epoetin beta,about 789 pM for NESP and about 982 pM for CERA.

In a further aspect of the present invention there is provided anErythropoiesis Stimulating Agent (ESA) for use in the treatment ofanemia, the treatment comprising the steps of

-   -   (a) Obtaining the level of hemoglobin in a patient suffering        from anemia,    -   (b) Calculating from the level of hemoglobin (Hb) in said        patient the number of initial ESA binding sites present in said        patient using a non-linear dynamic Hb ESA-EPO-R pathway model,        and    -   (c) Determining a therapeutically effective dosage of an ESA for        use in a treatment of anemia in said patient based on the number        of initial ESA binding sites in said patient as calculated in        (b).

The non-linear dynamic Hb ESA-EPO-R pathway model used in this aspecttakes into account the additional reactions of the production of Hbbased on the active ESA-EPO-R complex and a patients individual Hbdegradation.

The term “treatment” as used herein covers any treatment of a disease orcondition (e. g., anemia) in a mammal, particularly a human, andincludes: (i) preventing the disease or condition from occurring in asubject which may be predisposed to the disease but has not yet beendiagnosed as having it; (ii) inhibiting the disease or condition, i. e.arresting its development; or (iii) relieving the disease or condition,i. e. causing its regression or the amelioration of its symptoms.

As used herein, the term “therapeutically effective amount” refers tothat amount of a polymer-modified synthetic erythropoiesis stimulatingprotein which, when administered to a mammal in need thereof, issufficient to effect treatment (as defined above), for example, asinducer of red cell production, an anti-anemia agent, etc. The amountthat constitutes a “therapeutically effective amount” will varydepending on the ESA, the condition or disease and its severity, and thepatient to be treated, its weight, age, gender, etc., but may bedetermined routinely by one of ordinary skill in the art with regard tocontemporary knowledge and to this disclosure.

Administration of the ESA of the invention may be performed via anyaccepted systemic or local route known for the respective ESA, forexample, via parenteral, oral (particularly for infant formulations),intravenous, nasal, bronchial inhalation (i. e., aerosol formulation),transdermal or topical routes, in the form of solid, semi-solid orliquid or. aerosol dosage forms, such as, for example, tablets, pills,capsules, powders, liquids, solutions, emulsion, injectables,suspensions, suppositories, aerosols or the like. The erythropoiesisstimulating agents of the invention can also be administered insustained or controlled release dosage forms, including depotinjections, osmotic pumps, pills, transdermal (includingelectrotransport) patches, and the like, for the prolongedadministration of the polypeptide at a predetermined rate, preferably inunit dosage forms suitable for single administration of precise dosages.The compositions will include a conventional pharmaceutical carrier orexcipient and a protein antagonist or agonist of the invention and, inaddition, may include other medicinal agents, pharmaceutical agents,carriers, adjuvants, etc. Carriers can be selected from the variousoils, including those of petroleum, animal, vegetable or syntheticorigin, for example, peanut oil, soybean oil, mineral oil, sesame oil,and the like. Water, saline, aqueous dextrose, and glycols are preferredliquid carriers, particularly for injectable solutions. Suitablepharmaceutical carriers include starch, cellulose, talc, glucose,lactose, sucrose, gelatin, malt, rice, flour, chalk, silica gel,magnesium stearate, sodium stearate, glycerol monostearate, sodiumchloride, dried skim milk, glycerol, propylene glycol, water, ethanol,and the like. Other suitable pharmaceutical carriers and theirformulations are described in “Remington's Pharmaceutical Sciences” byE. W. Martin.

The inventors furthermore discovered the mathematical model of theinvention can be used to determine the biological activity of an ESAcandidate compound. Hence there is also provided a method for estimatingthe biological activity of an ESA, comprising the steps of:

-   (a) Calculating the occupancy of the EPO receptor on human CFU-E    cells in response to a range of ESA concentrations using the    non-linear dynamic pharmacokinetic (PK) ESA-EPO-R pathway model,-   (b) Calculating the area under the curve for the ESA from the    resultant of step (a) as a measure for EPO receptor occupancy of the    ESA,-   (c) Calculating the concentration of the ESA for which the half    maximum occupancy of the EPO receptor is reached to obtain an    EC50ESA,-   (d) Compare the EC50ESA with a predetermined EC50EPOalfa or    EC50EPOalfa,

Wherein the difference between the EC50ESA compared to the predeterminedEC50EPOalfa or EC50EPOalfa correlates with the difference of thebiological activity of the ESA when compared with the biologicalactivity of EPO alfa or EPO beta.

The biological activity of the ESA or EPO is preferably provided inUnits (U) per μg and described the ability of the ESA to induce bloodcell proliferation.

The EC50EPOalfa or EC50EPOalfa may be predetermined by performing inaddition steps (a) to (c) of the aforementioned method using EPO alfa orEPO beta as “ESA” to obtain in step (c) the values for EC50EPOalfa orEC50EPOalfa. The biological activity of EPO alfa or EPO beta is wellknown. Alternatively, other ESAs for which the biological activity isknown may be used as a reference.

In this aspect the non-linear dynamic pharmacokinetic (PK) ESA-EPO-Rpathway model as described herein is used.

Another aspect of the invention further An Erythropoiesis StimulatingAgent (ESA) for use in the treatment of anemia in a subject, thetreatment comprising the steps of

-   (a) Determining or providing hemoglobin concentrations in the    subject from at least two separate time points and calculating    therefrom a subject specific hemoglobin degradation rate,-   (b) Determining the present hemoglobin concentration in the subject,-   (c) Calculating from the subject specific hemoglobin degradation    rate and the hemoglobin concentration in the subject the dosage of    an ESA sufficient to treat the anemia in the subject using a    non-linear dynamic pharmacokinetic (PK) hemoglobin (Hb) ESA-EPO-R    pathway model, and-   (d) Administering to the subject the calculated dosage of the ESA as    determined in (c),-   (e) Optionally, monitoring the hemoglobin concentration in the    subject after administration of the ESA and adjusting the next    dosage of the ESA by repeating steps (b) to (d).

The invention also pertains to a computer implemented method fordetermining an ESA dosage for an anemia treatment in a subject, themethod comprising the steps of

-   (a) providing at least two separate hemoglobin concentrations of the    subject before the treatment,-   (b) calculating from the hemoglobin concentrations in (a) a subject    specific hemoglobin degradation rate,-   (c) calculating from the subject specific hemoglobin degradation    rate as deter-mined in-   (b) and from a present hemoglobin concentration in the patient, an    ESA dosage using a non-linear dynamic pharmacokinetic (PK)    hemoglobin (Hb) ESA-EPO-R pathway model.

The method may further comprise repeating step (c) for obtaining anadjusted next ESA dosage.

Finally there is provided a method for the stratification of an anemiapatient receiving ESA treatment, the method comprising the determinationof a patient specific hemoglobin degradation rate by monitoringhemoglobin concentration in the patient over time and calculatingtherefrom the patient specific hemoglobin degradation rate and, whereinan increased hemoglobin degradation rate in the patient compared to areference value indicates a decreased response to the ESA treatment, andwherein an increased hemoglobin degradation rate in the patient comparedto a reference value indicates that the patient is overdosed.

The present invention will now be further described in the followingexamples with reference to the accompanying figures and sequences,nevertheless, without being limited thereto. For the purposes of thepresent invention, all references as cited herein are incorporated byreference in their entireties. In the Figures:

FIG. 1: Characterization of ESA binding properties based on thedetermination of ligand depletion and the ESA-EpoR mathematical model.Parental BaF3 cells (BaF3) and BaF3 stably expressing the murine EpoR(BaF3-mEpoR) were incubated with 100 ρM Epo alfa or 100 ρM Epo beta. Atthe indicated times the supernatant was removed and the concentration ofEpo was quantified by an ELISA assay. Based on this data the associationrate k_(on), the dissociation rate k_(off) and the number of ESA bindingsides at the cellular surface (B_(max)) were estimated by the ESA-EpoRmathematical model and the ESA-specific dissociation constant K_(D)(k_(off)/k_(on)) was calculated. (a) BaF3 cells and BaF3 stablyexpressing the human EpoR (BaF3-hEpoR) were incubated with Epo alfa, Epobeta, NESP and CERA. At the indicated times the supernatant was removedand the concentration of Epo was quantified by an ELISA assay. Based onthis data the association rate k_(on), the dissociation rate k_(off) andthe number of ESA binding sides at the cellular surface (B_(max)) wereestimated by the ESA-EpoR mathematical model and the ESA-specificdissociation constant K_(D) (k_(off)/k_(on)) was calculated. (b)Predicted by the ESA-EpoR mathematical model for each ESA theassociation rate k_(on) was plotted against the dissociation ratek_(off). The calculated ESA-specific dissociation constant K_(D) for thehEpoR is indicated by symbols. Shaded areas around the symbols indicatethe confidence interval of the K_(D) (k_(off)/k_(on)). The heatmapdisplays the values of the K_(D).

FIG. 2: Presence of a functional EpoR on human lung cancer cell lines.(a) Total mRNA was extracted from the NSCLC cell lines H838, H1299, A549and H1944 and the expression of the EpoR mRNA was determined by qRT-PCR.The EpoR mRNA expression in H838 cells was used as reference. (b) BaF3cells and BaF3-hEpoR as well as the indicated NSCLC cell lines werestimulated with 10 U/ml of Epo beta for 10 min or were left untreatedand were lysed. The abundance of the phosphorylated EpoR (pEpoR) and thetotal EpoR was determined by immunoprecipitation (IP) and quantitativeimmunoblotting (IB). The experiment was performed in biologicaltriplicates and one representative immunoblot is shown. (c) The NSCLCcell lines H838, H1299, A549 and H1944 were stimulated with 4 pM of Epobeta and the Epo depletion kinetics was determined by an ELISA assay upto 8000 min incubation time. The ESA-EpoR mathematical model wasemployed to describe the depletion kinetics in all analyzed NSCLC celllines and to determine the number of ESA binding sites/cell (B_(max)).

FIG. 3: H838-EpoR cells can serve as a model for human CFU-E cellsconcerning EpoR levels (a) Human hematopoietic stem cells (hHSC) fromcord blood were isolated and differentiated to human CFU-E (hCFU-E) asdescribed. hCFU-E and hHSC cells that served as negative control (a) aswell as NSCLC cell line H838 stably transduced with hEpoR (H838-EpoR)(b) were stimulated with 4 pM of Epo beta and time-resolved analysis ofthe depletion kinetics was monitored via ELISA assay over the timeperiod of 200 min (experimental data-dots). The model could describe thedepletion kinetics (model-solid line) and estimate KD and Bmax values.(c) Quantitative immunoblot demonstrating overexpression level of humanEpoR in H838-hEpoR cells compared to parental H838. Functionality ofEpoR is shown by Epo-induced phosphorylation of receptor and JAK2.

FIG. 4: CERA preferentially activates cells with high EpoR expression(a) Model based prediction of differential dose response for EpoRactivation in H838-hEpoR by different ESAS (left panel). Blue and redlines correspond to Epo beta and CERA respectively. Dashed linesindicated the EC50 of each ESA in the activation of theerythroprogenitors, 141 ρM and 1048 ρM for Epo beta and CERArespectively. Right panel represents the validation of the modelprediction. Epo beta and CERA activates EpoR in a very different rangeof concentrations. H838-hEpoR cells were stimulated during 10 minuteswith increasing concentrations of each ESA. Cells were lysated, EpoRimmunoprecipitated and blotted against total and phosphorylated form.Blue circles represent experimental data upon Epo beta stimulation. Redcircles represent experimental data corresponding to CERA stimulation.Solid lines are the activation trajectories predicted by the model. (B)Left panel represents the model based prediction of the integral EpoRactivation by each EC50 during 60 minutes. Area under the curve shows nosignificant difference between Epo beta and CERA activation inH838-EpoR, Right panel shows the model based prediction of the integralEpoR activation by each EC50 during 60 minutes in H838. In this case thearea under the curve indicates a probable lower activation of EpoR byCERA in comparison with Epo beta.

FIG. 5: Differential pharmacokinetic behavior of CERA among healthy andNSCLC subjects. (a) Pharmacokinetic behavior of increasing CERAconcentrations in healthy volunteers. Colored circles are the meanvalues of CERA concentrations in serum, determined by ELISA assay. Solidlines represent the trajectories predicted of the CERA clearance for thegiven concentrations and the experimental data. (B) Pharmacokineticbehavior of increasing CERA concentrations in NSCLC patients in stageIII or IV. Colored circles are the mean values of CERA concentrations inserum, determined by ELISA assay. Solid lines represent the trajectoriespredicted of the CERA clearance for the given concentrations and theexperimental data. The different trajectories reported by the model,describes the experimental data and showed a reduction of 72%16% in theCERA clearance capability of NSCLC patients. (c) Characterization andrelative comparison of CERA clearance capability (% of CFU-E) of NSCLCpatients and healthy subjects. The dashed line is the 100% clearancecapability of CERA, which represents the normal capability of CERAclearance in healthy subjects. The pinky bars represent the number ofNSCLC patients with a define % of CERA clearance capability compared tohealthy subjects (individual PK data extracted from Hirsch et al 2007clinical trial). The plot represents a general reduction of CFU-Epopulation (% of CERA clearance capability) in NSCLC patients incomparison in comparison of the mean value in healthy subjectsrepresented as 100%. It can be also notice different grades of reductionin the CFU-E population of NSCLC patients.

FIG. 6: Graphical representation of the basic andpharmacokinetic/pharmacodynamic mathematical model. (a) the reactions 1to 6 are 1:Binding/unbinding of ESA to the Epo receptor (EpoR). Thek_(on)/k_(off) rate constants of the binding/unbinding reaction are ESAspecific and can be fully characterized using the trafficking model andthe respective depletion data. 2: ESA-EpoR complex internalization. 3:Recycling to the cell membrane and dissociation of the internalizedESA-EpoR complex. 4: Production/degradation of EpoR at the cellmembrane. The production/degradation reactions are in equilibriumdefining a certain, cell type (a)/patient (b) specific amount ofreceptors at the cell surface characterized by Bmax parameter. 5:Degradation of internalized ESA-EpoR complex. 6: Degradation and releaseof internalized ESA-EpoR complex; (b) additional reactions 7 to 9 are 7:Clearance in the blood compartment, 8: Transport into blood compartment,9: Saturable clearance in the interstitial compartment. (c) Calculationof B_(max) based on the Hb levels further includes the reactions 10:Production of Hb triggered by the activated receptor complex, and 11:depletion of Hb in the blood of an individual.

FIG. 7: CERA preferentially activates signal transduction in cells withhigh EpoR abundance. Quantification of STAT5 phosphorylation in H838 andhCFU-E cells upon Epo beta and CERA stimulation. H838 (left panel) andhCFU-E (right panel) cells were stimulated with 1331 pM of Epo beta and8841 pM of CERA corresponding to the half-maximal activation of STAT5phosphorylation in CFU-Es. Measurements of the degree of phosphorylatedSTAT5 (symbols) were performed by mass spectrometry. Solid linesindicate smoothing spline approximations.

FIG. 8: Individualized pharmacokinetics and pharmacodynamics in healthysubjects and NSCLC IIIB-IV patients treated with CERA. (a) Graphicalrepresentation of the equations (1 . . . 11) of the integrative (PK/PD)ESA-EpoR mathematical model using the cell designer formalism. Hb:hemoglobin, sc: subcutaneous, dESAi: intracellular degraded ESA; dESAe:extracellular degraded ESA. (b) The pharmacokinetics andpharmacodynamics of the NSCLC patient (ID:2101, CSR NA17101 clinicaltrial) is shown in purple. The amount and timing of the CERA dose givento this patient is displayed in the top panel. In the middle panel, thepharmacokinetics of CERA is indicated. The concentration of CERA in theblood stream of this patient at different time points is symbolized bydots and the trajectories of the mathematical model are indicated by asolid line. In the lower panel the pharmacodynamics of hemoglobin (Hb)is shown indicating the experimental measurements by dots and modeltrajectories by a solid line. The model predicted ESA binding sites perpatient and the Hb degradation rate are indicated. (c) Thepharmacokinetics and pharmacodynamics of the healthy subject (ID:25,WP16422 clinical trial) is shown in green. The amount and timing of theCERA dose given to this individual is shown in the top panel. In themiddle panel the pharmacokinetics of CERA displayed. The CERAconcentration in the blood stream is indicated by dots and the solidline represents the model trajectory. The pharmacodynamics of hemoglobin(Hb) is shown in the lower panel. Dots correspond to experimental dataand the solid line represents the model trajectory. The model predictedESA binding sites/patient and the Hb degradation rate is indicated. (d)The distribution of ESA binding sites per patient and of the hemoglobindegradation rate in healthy subjects and NSCLC patients. Thedistribution of the Hb degradation rate (left panel) and of the ESAbinding sites (Bmax) (right panel) in 88 healthy subjects (green) and 88NSCLC patients (purple) is depicted.

FIG. 9: NSCLC patient stratification and individualized treatmentrecommendation by the integrative PK/PD ESA-EpoR mathematical model. (a)CERA treatment simulations according to the patient-specific parametersin three patients of the CSR NA17101 clinical trial. Patient 1, 2 and 3correspond to ID2303, ID1022 and ID2652 respectively. Upper panelsrepresent the CERA dose and regimens given to patients based on thecurrent posology for NESP. Lower panels represent the outcome for thethree patients. Dashed lines correspond to the optimal outcome that canbe achieved within the limits of the current label for ESAs. Solid linerepresents the outcome for each patient predicted by the integrativePK/PD ESA-EpoR mathematical model. Shading represents the confidenceinterval of the model prediction for Hb levels. (b) Patientstratification based on the current ESA posology. The patient-specificESA binding sites per patient and the Hb degradation rates estimated bythe integrative PK/PD ESA-EpoR mathematical model for all patients inthe CSR NA17101 clinical trial are indicated by the symbols. Patient 1,2 and 3 studied in (a) are marked with black circles. Overdosed patientsare defined by a Hb increment >2 g/dl in four weeks and/or reaching Hblevels >13 g/dl and Non-treatable patients are characterized by noincrement of Hb levels during the treatment. (c) Model-based optimizedESA treatment of patient 1, 2 and 3. The upper panel represents the doseand regimens that the model recommends for each patient. The lower panelrepresents the model predicted treatment outcome for each patient.Dashed line corresponds to the ideal outcome based on the current labelfor ESAs. Solid line represents the outcome prediction by the model.Shading represents the assumed confidence interval of the Hbmeasurement. (d) Stratification of the 88 NSCLC IIIB-IV patients fromthe CSR NA17101 clinical trial. Patient 1, 2 and 3 are marked with ablack circle. The lines indicate the maximal CERA doses required tosuccessfully treat the respective patients at an interval of threeweeks, except for patients with a very high Hb degradation rate and ahigh number of ESA binding sites that require weekly CERA doses.

EXAMPLES

Materials and Methods

Plasmids and Reagents.

Retroviral expression vectors were pMOWS-puro (Ketteler et al., 2002).The generation of hemagglutinin (HA)-tagged murine Epo receptor(pMOWS-HA-mEpoR) and of HA-tagged human EpoR (pMOWS-HA-hEpoR) wasperformed as described previously (Becker et al., 2010). Cells wereeither treated with Epo alfa (Cilag-Jansen), Epo beta (Roche), NESP(Amgen), or CERA (Roche) at indicated concentrations.

Cell Culture and Transfection.

Human lung adenocarcenoma cell lines A549, H838, H1299, H1944, H1650,H1975 and H2030 were purchased by ATCC and cultivated in Dulbecco'smodified Eagle's Medium (DMEM, Lonza) supplemented with 10% fetal calfserum (FCS, Gibco) and 1% penicillin/streptomycin (Invitrogen). ThePhoenix eco and Phoenix ampho packaging cell lines (Kinsella & Nolan,1996) were cultured in DMEM (Gibco) supplemented with 10% FCS and 1%penicillin/streptomycin. BaF3 cells (Palacios & Steinmetz, 1985) werecultured in RPMI-1640 (Invitrogen) including 10% FCS and supplementedwith 10% WEHI conditioned medium as a source of IL-3. For the EpoRoverexpressing cell lines H838 (H838-hEpoR) and BaF3 (BaF3-mEpoR andBaF3-hEpoR) 1.5 μg/ml puromycin (Sigma) was added to the respectivemedium.

To obtain hCFU-E cells, CD34+ cells were sorted by MACS (CD34-MultisortKit, Miltenyi) from umbilical cord blood of healthy donors after writtenconsent. CD34+ cells were expanded using Stem Span SFEM II supplementedwith Stem Span CC110 (both StemCell Technology). After seven days ofexpansion cells were either washed extensively using IDMEM (Gibco) toremove cytokines and to initiate differentiation or cells were used fordepletion experiments. For differentiation cells were cultivated in StemSpan SFEM II supplemented with 10 ng/ml IL-3 (R&D Systems), 50 ng/ml SCF(R&D Systems) and 6 U/ml Epo alpha (Cilag-Jansen) as published byMiharada 2006. After 4 days of cultivation in this media hCFU-E wereharvested to perform depletion experiments. All cells were cultured at37° C. with 5% CO2 incubation.

Transfection of Phoenix eco and Phoenix ampho cells was performed bycalcium phosphate precipitation. Transducing supernatants were generated24 h after transfection by passing through a 0.45 m filter andsupplemented with 8 g/ml polybrene (Sigma). Stably transduced BaF3 cellsexpressing HA-tagged murine EpoR (BaF3-mEpoR cells) or HA-tagged humanEpoR (BaF3-hEpoR cells) or H838 cells expressing HA-tagged human EpoR(H838-hEpoR cells) were selected in the presence of 1.5 μg/ml puromycin(Sigma) 48 h after transduction. Surface expression of EpoR in BaF3 andH838-hEpoR cells was verified by Flow cytometry analysis.

Flow Cytometry.

EpoR surface expression was verified by flow cytometry. ThereforeH838-hEpoR cells were gently detached with Cell Dissociation Solution(Sigma) according to the manufacturer's instructions. BaF3-EpoR andH838-hEpoR cells were stained with anti-HA antibody (Roche) diluted 1:40in 0.3% PBS/BSA for 20 min at 4° C. Followed by washing of cells with0.3% PBS/BSA and incubation of secondary Cy5-labeled antibody againstrat (Jackson Immuno Research), diluted 1:100 in 0.3% PBS/BSA, for 20 minat 4° C. in the dark. After washing samples with 0.3% PBS/BSA, propidiumiodide (BD Biosciences) was added to exclude dead cells. Canto II (BDBioscience) was used for sample analysis.

Depletion Experiments and ELISA

ESA depletion experiments were conducted in NSCLC tumor cell lines,BaF3, BaF3-mEpoR, BaF3-hEpoR, hCFU-E, hHSC cells. Tumor cells wereseeded in 6 well-plates (TPP 92006) at a cellular concentration of 4×105cells in 3 ml of proliferating media (DMEM supplemented with 10% FCS and1%). Cells were kept at 37° C., 95% H2O and 5% CO2 during three days. Onthe third day cells were washed with DMEM (1% penicillin/streptomycinand 1 mg/ml BSA) and left them starving in 1 ml of washing media during12 hours. Cells were stimulated with Epo alfa/beta within the indicatedtimes and concentrations of the depletion plots. After the incubationtime, media was recovered and kept at −80° C. till the conclusion of theexperiment, cells were trypsinized and counted by hemoytometer chamber.Once the experiment was concluded ESAs concentration was measured byELISA (Quantikine IVD ELISA Kit, R&D DEP00).

The experimental setting for the depletion measurements was different inthe suspension cells; BaF3-hEpoR, BaF3-mEpoR, BaF3, hCFU-E and hHSC. Inthe transduced BaF3 cells, the experiments were conducted in between9-14 days of selection with puromicin (1.5 μg/ml). Cells were washedthree times in RPMI by centrifugation 5 minutes at 212×g, and starved 3hours in RPMI (1% penicillin/streptomycin and BSA 1 mg/ml) at aconcentration of 1×106 cells/ml. After the starvation period cells wereadjusted to a final concentration of 40×106 cells/ml in 350 μl at 37° C.and 900 rpm in a Thermomixer compact of Eppendorf. Cells were stimulatedby ESA during the indicated times in the plot and centrifuged during 5minutes, at 4° C. and 2500 rpm. Supernatant was removed and kept at −80°C. ESAs measurements were performed by ELISA (Quantikine IVD ELISA Kit,R&D DEP00). ESAs depletion measurements were conducted in the same wayin hCFU-E and hHSC with the only difference of the cell concentration30×106 cells/ml, and the used media (Stem Span SFEM II).

Immunoprecipitation and Quantitative Immunoblotting.

For analysis of phosphorylated and total proteins human lungadenocarcenoma cell lines as well as H838-hEpoR cell line were seeded,cultivated for 72 h, starved for 3 h in DMEM with 1%penicillin/streptomycin, 2 mM L-glutamine (Gibco) and 1 mg/ml BSA andthen stimulated with Epo beta or CERA at indicated concentrations for 10min. Prior to experiments BaF3 cells were washed and resuspended inserum-depleted RPMI-1640 supplemented with 1% penicillin/streptomycinand 1 mg/ml BSA and starved for 3 h. Afterwards the cells were harvestedand aliquoted in a density of 20×106/ml and stimulated with Epo beta atindicated concentrations for 10 min.

The cells were lysed with 1.25×NP-40 lysis buffer (1.25% NP-40, 187.5 mMNaCl, 25 mM Tris pH 7.4, 12.5 mM NaF, 1.25 mM EDTA pH 8.0, 1.25 mM ZnCl2pH 4.0, 1.25 mM MgCl2, 1.25 mM Na3VO4, 12.5% glycerol supplemented withaprotinin and AEBSF). The protein concentrations in lysates weremeasured using the colorimetric BCA protein assay kit (Pierce ProteinResearch Products). For Immunoprecipitation analysis the lysates(1500-2000 μg protein for lung adenocarcenoma cell lines, 400 μg proteinfor BaF3 cells) were supplemented with antibodies to EpoR (R&D, MAB307), JAK2 (Upstate) or STAT5A/B (Santa Cruz, C17) and Protein Asepharose (GE Healthcare) and rotated over night by 4° C.Immunoprecipitated proteins were separated by 10% SDS-PAGE andtransferred to nitrocellulose membrane (0.2 m pore, Schleicher &Schuell). For quantification purposes randomized non-chronological gelloading was performed (Schilling et al., 2005). For the detection of thephosphorylated proteins the blots were probed with mAbs specific forphosphotyrosine (pTyr) (Upstate, clone 4G10) and then with secondaryhorseradish peroxidase-coupled anti-mouse antibodies (Dianova). Toremove antibodies, membranes were treated as described previously(Klingmuller et al., 1995) and subsequently incubated with pAbs for EpoR(Santa Cruz, C-20) and horseradish peroxidase-coupled anti-rabbitantibodies (Dianova). Detection was performed using ECL substrate (GEHealthcare). Immunoblot data were acquired with the CCD camera-basedImageQuant LAS 4000 (GE Healthcare) and quantification was performedwith the ImageQuant TL version 7.0 software (GE Healthcare).

mRNA Isolation, cDNA Preparation and qPCR

For analysis of EpoR expression the cells were lysed and RNA extractionwas performed using RNeasy Mini kit (Qiagen) according to the supplier'sprotocol. To obtain cDNA from RNA, the high-capacity cDNA reversetranscription kit (Applied Biosystems) was used according tomanufacturer's instructions. Quantitative real-time PCR (qRT-PCR)analysis was performed using LightCycler 480 (Roche applied-Science).Samples were prepared with reagents of the LightCycler480 Probes MasterKit from Roche applied-Science. Specific primers were obtained fromEurofins MWG and universal probes (UPL) for TaqMan quantification of DNAfrom Roche applied-Science. Concentrations were normalized using thegeometric mean of 0-glucuronidase (GUSB) and esterase D (ESD). Primerstargeting human EpoR: forward-ttggaggacttggtgtgtttc;reverse-agcttccatggctcatcct; ESD: forward-ttagatggacagttactccctgataa;reverse-ggttgcaatgaagtagtagctatgat; GUSB: forward-cgccctgcctatctgtattc;reverse-tccccacagggagtgtgtag.

Mass Spectrometry Analysis.

Cellular lysate were subjected to IP with a combination of two STAT5antibodies, sc-1081 and sc-836 from Santa Cruz Biotechnology. Two IPswere pooled per lane. Proteins were separated by a 10% SDS-PAGE (GEHealthcare) in 1× Laemmli buffer (Laemmli 1970). Following coomassiestaining with SimplyBlue™ SafeStain (Invitrogen) STAT5 gel bands wereexcised at approximately 90 kDa and cut into small pieces (1 mm3). Gelpieces were destained, reduced with DTT (dithiothreitol, SIGMA),alkylated with IAA (iodoacetamide, SIGMA) and digested with 0.3 μgtrypsin in 100 mM NH4HCO3/5% acetonitrile buffer overnight. In-houseproduced one-source peptide/phosphopeptide ratio standards for STAT5Aand STAT5B were added to the digests (Boehm 2014). Following a four-steppeptide extraction performed sequentially with 100 mM NH4HCO3/5%acetonitrile, acetonitrile, 5% formic acid, and acetonitrile, thesamples were concentrated in a speedvac (Eppendorf) and desalted withC18 Ziptips (Millipore) using solutions based on water, acetonitrile andformic acid. Samples were analyzed by EASY-nLC 1000 (Thermo Scientific)coupled to a Q Exactive™ Hybrid Quadrupole-Orbitrap Mass Spectrometer(Thermo Scientific). As precolumn we used Acclaim PepMap 100, 75 μm×2cm, as analytical column we used Acclaim PepMap RSLC C18, 2 μm, 100 Å,75 μm×25 cm. Survey full scan MS spectra were acquired at resolutionR=70,000 and analyzed for the native and labelled STAT5 peptide andphosphopeptide pairs with Xcalibur 3.0.63 (Thermo).

The in vitro trafficking model (FIG. 6a ) was extended to apharmacokinetic/pharmacodynamics (PK/PD) model (FIG. 6b ) by includingblood and interstitium compartments and patient specific PK dataobtained by either intravenous (IV) or subcutaneous (SC) injections ofESA/CERA. Additionally, the model provides the link between ESA bound tothe EpoR (ESA_EpoR) and haemoglobin levels (Hb) measured in patients.The model consists of the following additional reactions:

-   -   7. Clearance in the blood compartment.    -   8. Transport into blood compartment.    -   9. Saturable clearance in the interstitial compartment.    -   10. Production of Hb triggered by the activated receptor        complex.    -   11. Patient specific degradation of Hb.

The reaction rate equations are given by:

-   -   1. “k_(on)*ESA*EpoR” and “k_(off)*ESA_EpoR”    -   2. “k_(e)*ESA_EpoR”    -   3. “k_(ex)*ESA_EpoR_i”    -   4. “k_(t)*Bmax” and “k_(t)*EpoR”    -   5. “k_(di)*ESA_EpoR_i”    -   6. “k_(de)*ESA_EpoR_i”    -   7. “k_(clear)*ESA”    -   8. “k_(scout)*ESA_SC”    -   9. “k_(scclear)*ESA_SC/(k_(scclearsat)+ESA_SC)”    -   10. “k_(hb_pro)*ESA_EpoR”    -   11. “k_(hb_deg)*Hb”

Model Calibration

For calibration of the model parameters, the inventors used the D2Dsoftware package (Raue et al. PloS ONE 2013) in MATLAB (Release 2012b,The MathWorks, Inc., Natick, Mass., USA). In order to minimize thedistance between the simulated model trajectories and the measured data,a maximum likelihood approach was applied. The inventors used adeterministic optimization algorithm combined with multiple startingpoints in the high dimensional parameter space to find the globaloptimum of the negative log-likelihood. As the parameter values canrange over several orders of magnitude and are, by its biochemicaldefinition, strictly positive, the optimization was performed inlogarithmized parameter space. To account for the log-normallydistributed measurement noise of protein time course data (Kreutz et al.Bioinformatics 2007), also the data were transformed onto thelogarithmic scale and an additive error model was fitted simultaneouslywith the kinetic model parameters. (Raue et al. PloS ONE 2013)

The affinity parameters (k_(on), k_(off) or k_(on) and k_(D)) and thenumber of binding sites (B_(max)) were estimated individually for eachexperimental condition, i.e. combination of ESA and cell type, as theydepend on the biochemical properties of the ESA and on the EpoRexpression level of the respective cell type.

The structural and practical identifiability of the parameters wasanalyzed using the profile likelihood approach as described by Raue etal. (Bioinformatics 2011). Furthermore, this method enabled theinventors to determine the parameter's confidence intervals and theuncertainties of the model predictions.

Example 1: Model Based Determination of ESA Binding Properties

To assess the role of Epo and Epo derivatives in the context of lungcancer, it was essential to develop a reliable, quantitative assay thatenables to determine the number of binding sides per cell and thespecific binding properties of different human ESA (Epo alpha, Epo beta,NESP and CERA). The inventors utilized our knowledge that rapid liganddepletion is characteristic for the Epo-EpoR system (Becker et al 2010)and established a robust ELISA assay to monitor Epo removal fromcellular supernatants.

As shown in FIG. 1a this enabled us to accurately quantify the depletionof Epo alfa and Epo beta by murine BaF3 cells stably expressing themurine EpoR (BaF3-mEpoR) whereas parental BaF3 cells had no impactunderscoring the specificity of the assay. These quantifications incombination with our dynamic pathway model of Epo-EpoR interactions(Becker et al 2010) enabled to calculate the dissociation constant K_(D)(FIG. 1a ) as well as the association rate k_(on), the dissociation ratek_(off) and the number of binding sides (B_(max)) for Epo alfa and Epobeta interaction with the murine EpoR.

The estimated B_(max) was in good agreement with the results obtained bytraditional saturation binding assays using radioactively labelledligand, further validating the assay. To comparatively examine thebinding properties of different ESAs for the human EpoR, the inventorsmeasured ESA depletion by BaF3 cells stably expressing the human EpoR(BaF3-hEpoR) or parental BaF3 cells (FIG. 1b ). The results showed thatwhereas Epo alpha and Epo beta are very rapidly depleted, depletion ofNESP and CERA is moderate. The quantitative time-resolved data incombination with our dynamic pathway model of ligand-receptorinteraction enabled us to calculate that K_(D) of Epo alpha and Epobeta, respectively, are with 16 and 17 pM very similar. However, forNESP the model indicates a K_(D) of 789 pM and for CERA a K_(D) of 982pM suggesting for both Epo derivatives a much elevated dissociationconstant.

Relating the K_(D) of the different ESA to the respective associationand dissociation rates as shown in FIG. 1c reveals that the associationof NESP and CERA is much slower compared to Epo alpha and Epo betawhereas the dissociation rate is enhanced. Therefore by combining simpletime-resolved quantification of the concentration of Epo in cellsupernatants with our dynamic pathway model it was possible to reliablydetermine the binding properties of ESA and to show that the availableESA differ significantly in their properties to bind to the human EpoR.

Example 2: Presence of Functional EpoR in NSCLC Cell Lines

To determine the presence of a functional EpoR in lung cancer cells, theinventors first screened a panel of NSCLC cell lines for the presence ofEpoR mRNA. Among these we identified three adenocarcinoma NSCLC celllines that showed significant levels of EpoR mRNA transcripts. Asdepicted in FIG. 2a H838 and H1299 showed moderate expression levels ofEpoR mRNA and A549 low levels. H1944 represent NSCLC cell lines withlevels below the detection limit (FIG. 2a ). Next evaluated was theexpression of the EpoR protein in the four selected NSCLC cell lines aswell as its functionality. Enrichment by immunoprecipitation anddetection by immunoblotting revealed the presence of the EpoR protein inH838 and H1299 and at very low levels in A549, whereas it was absent inH1944 (FIG. 2b ). In line with previous observations the overallexpression level of EpoR protein was very low compared to BaF3-hEpoR.

Upon stimulation with Epo as expected the tyrosine phosphorylated formof the receptor was absent in parental BaF3 cells and H1944, but evidentin H838, H1299 and A549 indicating the presence of a signalingcompetent, functional EpoR in these three NSCLC cell lines. To determinethe binding properties of the EpoR expressed in the NSCLC cell lines,the inventors applied the depletion assay and showed (FIG. 2c ) that Epobeta was depleted by the NSCLC cell lines harboring a functional EpoR,but not by the EpoR negative NSCLC cell line H1944 (FIG. 1b ). However,Epo beta depletion was much slower compared to BaF3-EpoR cellssuggesting the presence of a significantly lower number of cell surfacereceptors. Accordingly, analysis of the time-resolved data with thedynamic pathway model revealed binding sides ranging from undetectableto 90 per cell (FIG. 2c and Table 2), yet the estimated K_(D) wascomparable to the estimates with BaF3-hEpoR. This shows that liganddepletion and signaling competent receptor is present on a subset ofNSCLC cell lines.

Example 3: EpoR Depletion Kinetics in Cells with High Numbers of EpoR

The main target of Epo treatment during anemia are erythroid progenitorcells at the colony forming units-erythroid (CFU-E) stage that expresshigh levels of the EpoR. To quantify the cell surface expression of theEpoR on human CFU-E and characterize the binding properties, human CD34+hematopoietic stem cells (hHSC) were prepared from human umbilical cordblood and differentiated to human CFU-E (hCFU-E). Time-resolved analysisof Epo beta depletion revealed rapid reduction of Epo beta from thesupernatants of hCFU-E but not of hHSC that lack the EpoR (FIG. 3a ).Model based analysis showed a K_(D) comparable to BaF3-hEpoR and aB_(max) of 365 binding sites per cell that was one order of magnitudelower compared to BaF3-hEpoR but one order of magnitude higher incomparison to the NSCLC cell line H838.

To examine whether some of the available ESA could have advantages inthe tumor context due to the distinct binding properties, the inventorsaimed at establishing a cell model system with elevated hEpoR expressionlevels mimicking the situation in hCFU-E as hCFU-E are only available atextremely limiting amounts. The inventors stably expressed the hEpoR inH838 (H838-hEpoR) and showed by enrichment using immunoprecipitation andimmunoblotting that the expression of the EpoR was highly increased andthe phosphorylated EpoR was substantially elevated (FIG. 3b ). Depletionexperiments and model-based analysis revealed binding properties rathersimilar to hCFU-E (FIG. 3c ) establishing the H838-hEpoR cell line assuitable model system to examine the impact of different ESA on cellsharboring high levels of the EpoR as observed in the hematopoieticsystem versus cells expressing low levels as in the tumor context.

Example 4: Identification of CERA as an ESA Preferentially ActivatingCells with High EpoR Expression

To compare the impact of ESA on tumor cells that express low levels ofEpoR versus cells that display elevated EpoR levels such as H838-EpoR,model simulations were performed. As readout for EpoR signaling, wecalculated the integral of ESA bound to the EpoR (ESA_EpoR) for thefirst 60 minutes after stimulation. First these stimulations wereperformed for different ESA concentrations and predicted the EC₅₀ forboth Epo beta and CERA in cells with high EpoR levels (FIG. 4a ). Themodel predicts that a 10-fold higher concentration of CERA is requiredfor the same activation. This model prediction was experimentallyvalidated in H838-EpoR cells by quantitative immunoblotting againstphosphorylated EpoR.

Interestingly, the model predicted that the ESA concentrations thatinduce the same activation in cells with high EpoR levels actdifferently in cells with low levels of EpoR such as H838. As thesecells deplete less Epo beta, Epo beta results in stronger activationthan CERA in cells with low levels of EpoR (FIG. 4b ). Experimentallythis model prediction was validated in H838 cells by quantitative massspectrometry against phosphorylated STAT5. Thus, CERA was identified asan ESA preferentially activating cells with high EpoR expression, suchas H838-EpoR and hCFU-E cells, rather than cells with low EpoRexpression, such as NSCLC cells.

Example 5: Determination of the Number of CFU-E Cells in HealthySubjects and NSCLC Patients by an Integrated PK/PD Model

Having identified CERA as an ESA preferentially acting on cells withhigh EpoR levels, we integrated our model with pharmacokinetic (PK) datato describe CERA dynamics in patients (the integrative (PK/PD) ESA-EpoRmathematical model; see above). In a first step, the inventors analyzedmean PK values of CERA in the serum of healthy subjects (Locatelli etal.) as well as of NSCLC stage IIIB-IV patients (Hirsh et al). As CERA,which is pegylated, is not cleared by the kidney, it was hypothesizedthat the clearance of CERA in the blood stream is only accomplished bybinding to EpoR and internalization, as seen in the in vitroexperiments. Furthermore, it was assumed that the main differencebetween healthy subjects and NSCLC patients in Epo dynamics is thenumber of CFU-E cells, which may be reduced by the tumor load and by thechemotherapy. Indeed, these assumptions were sufficient to describe theexperimental PK data for both healthy subjects (FIG. 5a ) and cancerpatients (FIG. 5b ). Furthermore, the model determined a decrease of 72%in the average number of CFU-E cells in the NSCLC stage IIIB-IVpatients, resulting in longer clearance times of CERA.

Then, the inventors applied the same approach to PK data of individualNSCLC patients. While the data appears very heterogeneous, the modelcould again describe all data sets based only on different numbers ofESA binding sites, i.e. CFU-E cells. While ESA binding sites may also bepresent on other cells, such as the NSCLC cells, they will notcontribute significantly to clearance of CERA due to their lowexpression levels. Importantly, it was possible to determine the numberof CFU-E cells for each cancer patient, showing a highpatient-to-patient variability (FIG. 5c ).

Example 6: Determination of the Number of CFU-E Cells in HealthySubjects and NSCLC Patients Based on the Patient Hemoglobin (Hb) Levels

The above model was also able to correlate the hemoglobin (Hb)increments with the PK/PD data in individualized patient data sets.

In particular, the in vitro trafficking model (FIG. 6A) was extended toa pharmacokinetic/pharmacodynamics (PK/PD) model (FIG. 6B) by includingblood and interstitium compartments and patient specific PK dataobtained by either intravenous (IV) or subcutaneous (SC) injections ofESA/CERA. The PK profiles correlates with the number of CFU-E and thisnumber with the recovery of the anemia, indicated by Hb levels. Theinventors established the correlation between the individual patienthistories with the PK profiles and these ones with the number of CFU-Eper patients, and these ones with the outcome of the ESA treatment(increment of Hb levels). The Hb model includes therefore the additionalreactions of the production of Hb by active ESA-EPO-R signalling sincethe ESAEPO-R signalling induces the maturation of erythrocytes thattherefore increases Hb concentrations (FIG. 6C). Additionally, the modelincludes the patient specific degradation of Hb, which is easilydetermined in anemic patients, because there Hb status is regularlymonitored.

Example 7: CERA Preferentially Activates Cells with High EpoR Expression

We examined the impact of ESA binding properties and of different ESAbinding sites on receptor activation to assess whether some of theavailable ESAs could have advantages in the tumor context. The ESA-EpoRmathematical model predicted that ESA concentrations that induce thesame degree of activation of signaling in cells with high EpoR abundanceact differently in cells with low levels of the EpoR (FIGS. 4a and 4b ).This behavior was experimentally validated in H838 and hCFU-E cells bymass spectrometric analysis of STAT5 phosphorylation in response tostimulation with Epo beta or CERA (FIG. 7). H838 and hCFU-E werestimulated with 1331 pM of Epo beta or 8841 pM of CERA, concentrationsthat correspond to the half-maximal activation of STAT5 phosphorylationin hCFU-Es. As the ESA-EpoR mathematical model predicted (FIG. 4), theactivation of EpoR signaling by CERA is less effective in cells with lowlevels of the EpoR such as NSCLC cells (FIG. 7 left panel) compared tocells with higher levels of the EpoR like hCFU-E (FIG. 7 right panel).Thus, we identify CERA as an ESA preferentially activating erythroidprogenitor cells rather than tumor cells.

Example 8: Integrative PK/PD ESA-EpoR Model-Based Stratification ofNSCLC Patients

As in example 5, we applied the same approach to the PK/PD data fromindividual NSCLC patients (clinical trial CSR NA17101) and healthysubjects (clinical trial WP16422). Although the patient data isapparently very heterogeneous, the integrative PK/PD ESA-EpoR model(FIG. 8a ) is able to describe all patient data sets. Herein weexemplify two individual cases, NSCLC patient ID:2101 (clinical trialCSR NA17101) (FIG. 8b ) and healthy subject ID:25 (clinical trialWP16422) (FIG. 8c ). The integrative PK/PD ESA-EpoR model was able todescribe the time-course of CERA concentrations determined in the serumand the corresponding Hb levels measured in the blood in response to theindicated ESA regimen, (FIGS. 8b and c ). To describe the heterogeneousPK/PD data, we assume that in addition to the different number of ESAbinding sites, already explained in example 5, the net loss of Hb(KHb_deg) could be another key difference between healthy subjects andNSCLC patients. Due to the inflammation associated with cancer, thehalf-life of erythrocytes is shortened and could therefore affect theKHb_deg in particular in cancer patients. Indeed, this assumption wassufficient to describe the experimental PD data for both cancer patientsand healthy subjects (FIGS. 8b and c lower panels).

Importantly, we can estimate the number of ESA-binding sites forindividual cancer patients, showing a high patient-to-patientvariability and a very different distribution from the healthy subjects(FIG. 8d right). Further, the distribution of the estimated KHb_degparameter differs widely in healthy subjects and NSCLC patients (FIG. 8dleft panel).

Example 9: Model-Based Treatment Optimization in NSCLC Anemia

The current guidelines defined by the European Medicines Agency (EMEA)recommend that the hemoglobin (Hb) response to ESA treatment of anemiain cancer should neither exceed increments of Hb≥2 g/dl in the followingfour weeks after the first ESA dose nor should Hb levels reach highervalues than 13 g/dl. These guidelines recommend doubling the ESA dose ifthere is no response to the treatment (Hb increments ≤1 g/dl in 4 weeksafter the first ESA dose), or reducing the ESA dose by 25% or 50% if theincrement of Hb levels is ≥2 g/dl after four weeks and/or if Hb valuesranging from 12 g/dl to 13 g/dl are reached. Interruption of thetreatment is mandatory if the Hb value is higher than 13 g/dl. Weemployed the integrative PK/PD ESA-EpoR mathematical model to calculatedthe EC50 (ESA concentration required to obtain half-maximum EpoRoccupancy) for each ESA and determined the CERA doses that correspond tothe current guidelines for NESP. Considering the EMEA-recommended ESAguidelines, we performed CERA treatment simulations based on thepatient-specific parameters in three NSCLC patients (FIG. 9a ). In thecase of Patient 1 (ID:2303 CSR NA17101) the maximum CERA dose(equivalent to maximal NESP dose in the guidelines) would be given everythree weeks (FIG. 9a upper left panel), and the model predicts noresponse within the current ESA guidelines (FIG. 9a lower left panel).In Patient 2 (ID:1022 CSR NA17101) the model predicts a fasthematological response within the current ESA guidelines (FIG. 9a upperand lower middle panels). In Patient 3 (ID:2652 CSR NA17101) the modelpredicts an interruption of the ESA treatment (FIG. 9a upper rightpanel) due to overshooting Hb values in response to the treatment withinthe current ESAs guidelines (FIG. 9a lower right panels).

To understand the impact of the current ESA guidelines in the NSCLCanemia treatment, 88 patients from the CSR NA17101 clinical trial wereplotted based on patient-specific ESA binding sites and the Hbdegradation rates. Patient stratification was carried out by responseprediction within the current EMEA-recommended ESA guidelines (FIG. 9b). We defined as overdosed patients that were predicted to have an Hbincrement >2 g/dl in four weeks and/or reaching Hb levels >13 g/dl, suchas Patient 3 (ID:2652 CSR NA17101). We defined patients as treatable ifthey were predicted to have an Hb increment of ≤2 g/dl in four weeks andreach Hb levels of 12 g/dl, such as Patient 2 (ID:1022 CSR NA17101). Wedefined patients as non-treatable if they are predicted to have noincrement of Hb levels during the treatment, such as Patient 1 (ID:2303CSR NA17101). Interestingly, the integrative PK/PD ESA-EpoR mathematicalmodel predicted a systematic overdosing of a large fraction of NSCLCIIIB-IV patients treated within the EMEA-recommended ESA guidelines foranemia in cancer (FIG. 9b ).

The integrative PK/PD ESA-EpoR mathematical model can optimize the ESAdosing and scheduling to achieve a hematological response within thelimits of the ESAs guidelines for most of the NSCLC IIB-IV patients,minimizing the risk of overdosing (FIG. 9c ). For Patient 2 and 3, themodel is able to optimize the ESA regimens (FIG. 9c middle and rightupper panel) that result in hematological responses without compromisingthe safety limits (FIG. 9c middle and right lower panels). In theparticular case of Patient 1, the model recommended an ESA regimenbeyond the ESA guidelines (FIG. 9c left upper panel) to achieve ahematological response (FIG. 9c left lower panel). Finally, we displayedthe prediction for all ESA regimens required to effectively treat allthe NSCLC IIIB-IV patients of the CSR NA17101 clinical trial (FIG. 9d ).

1. A method for determining a dosage of an Erythropoiesis StimulatingAgent (ESA) that is sufficient for treating anemia in a patient, themethod comprising the steps of: a) Calculating a degradation ofhemoglobin per time for the patient from a hemoglobin concentration ofthe patient from at least two separate time points, b) Determining apresent hemoglobin concentration of the patient from a concentration ofhemoglobin from a recent blood sample obtained from the patient, c)Calculating an ESA dosage based on the degradation of hemoglobin pertime and the present hemoglobin concentration to treat anemia in thepatient; and d) Administering the ESA dosage to the patient to therebytreat anemia in the patient.
 2. (canceled)
 3. The method according toclaim 1, wherein the hemoglobin concentration of the patient from atleast two separate time points is determined by measuring the hemoglobinconcentrations in blood samples obtained from the patient from at leasttwo different time points, or from a past anemia treatment history ofthe patient.
 4. The method of claim 1, further including the step of:Monitoring the hemoglobin concentration of the patient over time afterthe administration of the ESA dosage.
 5. The method of claim 1, whereinthe administration is a subcutaneous or intravenous injection.
 6. Themethod of to claim 4, wherein the hemoglobin concentration of thepatient is monitored by obtaining a blood sample from the patient. 7.The method of claim 1, further including the steps of: a) Monitoring theclearance of said ESA dosage from a serum in said patient, b)Calculating from the clearance of said ESA dosage in said patient thenumber of initial ESA binding sites present in said patient using anon-linear dynamic pharmacokinetic (PK) ESA-EPO-R pathway model, and c)Adjusting the ESA dosage administered to the patient in accordance withthe number of ESA binding sites.
 8. (canceled)
 9. (canceled)
 10. Themethod of claim 7, wherein the ESA dosage is administeredsubcutaneously, and wherein the non-linear dynamic pharmacokinetic (PK)ESA-EPO-R pathway model considers clearance of the administered ESA in ablood compartment, transport of the administered ESA from aninterstitial compartment into the blood compartment, and clearance ofthe ESA in the interstitial compartment.
 11. The method of claim 1,wherein the ESA dosage is selected from the group of an Epoetin alfadosage, an Epoetin beta dosage, an erythropoiesis stimulating proteindosage and a Continuous erythropoietin receptor activator dosage. 12.The method of claim 7, wherein said non-linear dynamic pharmacokinetic(PK) ESA-EPO-R pathway model is based on a system of the ordinarydifferential equations (ODE): $\begin{matrix}{\frac{d\lbrack{ESASC}\rbrack}{dt} = {{{- {ksc}_{clear}} \cdot {\lbrack{ESASC}\rbrack/\left( {k_{{sc\_ clear}{\_ sat}} + \lbrack{ESASC}\rbrack} \right)}}\; - {{ksc\_ out} \cdot \lbrack{ESASC}\rbrack}}} & \left( {2.1.} \right) \\{\frac{d\lbrack{ESA}\rbrack}{dt} = {{k_{{sc}_{out}} \cdot \lbrack{ESASC}\rbrack} - {{k{clear}} \cdot \lbrack{ESA}\rbrack} - {k_{on} \cdot \lbrack{ESA}\rbrack \cdot \lbrack{EpoR}\rbrack} + {k_{off} \cdot \lbrack{ESAEpoR}\rbrack} + {k_{ex} \cdot \lbrack{ESAEpoRi}\rbrack}}} & \left( {2.2.} \right) \\{\frac{d\lbrack{EpoR}\rbrack}{dt} = {{{- k_{on}} \cdot \lbrack{ESA}\rbrack \cdot \lbrack{EpoR}\rbrack} + {k_{off} \cdot \lbrack{ESAEpoR}\rbrack} + {k_{t} \cdot B_{\max}} - {k_{t} \cdot \lbrack{EpoR}\rbrack} + {k_{ex} \cdot \lbrack{ESAEpoRi}\rbrack}}} & \left( {2.3.} \right) \\{\frac{d\lbrack{ESAEpoR}\rbrack}{dt} = {{k_{on} \cdot \lbrack{ESA}\rbrack \cdot \lbrack{EpoR}\rbrack} - {k_{off} \cdot \lbrack{ESAEpoR}\rbrack} - {k_{e} \cdot \lbrack{ESAEpoR}\rbrack}}} & \left( {2.4.} \right) \\{\frac{d\lbrack{ESAEpoRi}\rbrack}{dt} = {{k_{e} \cdot \lbrack{ESAEpoR}\rbrack} - {k_{ex} \cdot \lbrack{ESAEpoRi}\rbrack} - {k_{di} \cdot \lbrack{ESAEpoRi}\rbrack} - {k_{de} \cdot \lbrack{ESAEpoRi}\rbrack}}} & \left( {2.5.} \right) \\{\frac{d\lbrack{dESAi}\rbrack}{dt} = {k_{di} \cdot \lbrack{ESAEpoRi}\rbrack}} & \left( {2.6.} \right) \\{{\frac{d\lbrack{dESAe}\rbrack}{dt} = {k_{de} \cdot \lbrack{ESAEpoRi}\rbrack}},} & \left( {2.7.} \right)\end{matrix}$ where, ESA is Erythropoiesis-stimulating agent inmedium/blood, EpoR is Erythropoietin receptor, ESA EpoR is a complex ofESA bound to EpoR on the cell surface, ESAEpoR_(i) is an internalizedcomplex of ESA bound to EpoR, dESA_(i) is intracellular degraded ESA,dESA_(e) is extracellular degraded ESA, ESA_(SC) is ESA in thesubcutaneous compartment, k_(sc_clear) is ESA clearance in thesubcutaneous compartment, k_(sc_clear_sat) is saturation of ESAclearance in the subcutaneous compartment, K_(sc_out) is an ESAtransportation constant to the blood compartment, k_(clear) is an ESAclearance constant in the blood compartment, k_(on) is an ESA-EpoRassociation rate/on-rate, k_(off) is an ESA-EpoR dissociationrate/off-rate, k_(t) is a ligand-independent receptor turnover rate,k_(e) is an ESA-EpoR complex internalization constant, k_(ex) is an ESAand EpoR recycling constant, k_(di) is an intracellular ESA degradationconstant, k_(de) is an extracellular ESA degradation constant, andwherein B_(max) is the number of initial ESA binding sites per cell/perpatient.
 13. A method for identifying an Erythropoiesis StimulatingAgent (ESA) having a specific activity for cells with a high cellsurface expression of Erythropoietin-receptor (EPO-R), comprising thesteps of: a) Obtaining the half maximal effective concentrations (EC50)of a candidate ESA and a reference ESA for EPO-R activation in a firstcell, b) Obtaining the EPO-R activation induced by the candidate ESA andthe reference ESA at their respective EC50 as obtained in (a) in asecond cell, wherein said second cell is characterized by asignificantly lower cell surface expression of EPO-R compared to thefirst cell, wherein a decreased activation of EPO-R in said second cellby the candidate ESA compared to the activation of EPO-R in said secondcell by the reference ESA, is indicative for the specificity of saidcandidate ESA for cells with a strong cell surface expression of EPO-R.14. The method according to claim 13, wherein said reference ESA isEpoetin beta.
 15. The method according to claim 13, wherein the methodis an in-vitro or an in-silico method.
 16. The method according to claim15, wherein the method is the in-silico method and wherein said EPO-Ractivation is calculated with a non-linear dynamic ESA-EPO-R pathwaymodel.
 17. The method according to claim 16, wherein said non-lineardynamic ESAEPO-R pathway model is based on the following ODE:$\begin{matrix}{\frac{d\lbrack{ESA}\rbrack}{dt} = {{{- k_{on}} \cdot \lbrack{ESA}\rbrack \cdot \lbrack{EpoR}\rbrack} + {k_{off} \cdot \lbrack{ESAEpoR}\rbrack} + {k_{ex} \cdot \lbrack{ESAEpoRi}\rbrack}}} & \left( {1.1.} \right) \\{\frac{d\lbrack{EpoR}\rbrack}{dt} = {{{- k_{on}} \cdot \lbrack{ESA}\rbrack \cdot \lbrack{EpoR}\rbrack} + {k_{off} \cdot \lbrack{ESAEpoR}\rbrack} + {k_{t} \cdot B_{\max}} - {k_{t} \cdot \lbrack{EpoR}\rbrack} + {k_{ex} \cdot \lbrack{ESAEpoRi}\rbrack}}} & \left( {1.2.} \right) \\{\frac{d\lbrack{ESAEpoR}\rbrack}{dt} = {{k_{on} \cdot \lbrack{ESA}\rbrack \cdot \lbrack{EpoR}\rbrack} - {k_{off} \cdot \lbrack{ESAEpoR}\rbrack} - {k_{e} \cdot \lbrack{ESAEpoR}\rbrack}}} & \left( {1.3.} \right) \\{\frac{d\lbrack{ESAEpoRi}\rbrack}{dt} = {{k_{e} \cdot \lbrack{ESAEpoR}\rbrack} - {k_{ex} \cdot \lbrack{ESAEpoRi}\rbrack} - {k_{di} \cdot \lbrack{ESAEpoRi}\rbrack} - {k_{de} \cdot \lbrack{ESAEpoRi}\rbrack}}} & \left( {1.4.} \right) \\{\frac{d\lbrack{dESAi}\rbrack}{dt} = {k_{di} \cdot \lbrack{ESAEpoRi}\rbrack}} & \left( {1.5.} \right) \\{{\frac{d\lbrack{dESAe}\rbrack}{dt} = \; {k_{de} \cdot \lbrack{ESAEpoRi}\rbrack}}\;,\; {{wherin}\mspace{11mu} B_{\max}\mspace{14mu} {is}\mspace{14mu} {the}{\mspace{11mu} \;}{number}{\; \;}{of}\mspace{14mu} {initial}\mspace{11mu} {ESA}\mspace{11mu} {binding}\mspace{11mu} {sites}}} & \left( {1.6.} \right)\end{matrix}$ where, ESA is Erythropoiesis-stimulating agent inmedium/blood, EpoR is Erythropoietin receptor, ESA EpoR is a complex ofESA bound to EpoR on the cell surface, ESAEpoR_(i) is an internalizedcomplex of ESA bound to EpoR, dESA_(i) is intracellular degraded ESA,dESA_(e) is extracellular degraded ESA, ESA_(SC) is ESA in thesubcutaneous compartment, k_(sc_clear) is ESA clearance in thesubcutaneous compartment, k_(sc_clear) sat is saturation of ESAclearance in the subcutaneous compartment, K_(sc_out) is an ESAtransportation constant to the blood compartment, k_(clear) is an ESAclearance constant in the blood compartment, k_(on) is an ESA-EpoRassociation rate/on-rate, k_(off) is an ESA-EpoR dissociationrate/off-rate, k_(t) is a ligand-independent receptor turnover rate,k_(e) is an ESA-EpoR complex internalization constant, k_(ex) is an ESAand EpoR recycling constant, k_(di) is an intracellular ESA degradationconstant, k_(de) is an extracellular ESA degradation constant.
 18. Themethod according to claim 15, wherein the method is the in-vitro method,and wherein said first cell is a cell ectopically expressing EPO-R, suchas H838-EpoR, and/or wherein said second cell is not ectopicallyexpressing EPO-R, such as H838.
 19. A computer implemented method forassessing the number of ESA binding sites in a cell, or a an organism,the method comprising (a) Obtaining the depletion rate of an ESA in saidcell or the organism, (b) Calculating the amount of ESA binding sites insaid cell or organism based on the depletion rate of the ESA using anon-linear dynamic EPO-R pathway model.
 20. The method according toclaim 19, wherein said organism is a patient or wherein said cell is acell endogenously expressing the EPO-R receptor, and wherein the cell isa red blood cell precursor cell, or a tumor cell, or a cell ectopicallyexpressing EPO-R.
 21. The method according to claim 19, wherein thepatient is a human patient, and wherein step (a) constitutes theobtaining the depletion rate of an ESA as acquired in a serum sample ofa patient at a time point subsequent to the administration of an initialESA dose to said patient, and step (b) constitutes calculating theamount of ESA binding sites based on the depletion rate of the ESA usinga non-linear dynamic pharmacokinetic (PK) ESA-EPO-R pathway model.22-24. (canceled)
 25. A method for estimating the biological activity ofan ESA, comprising the steps of: Calculating the occupancy of the EPOreceptor on human CFU-E cells in response to a range of ESAconcentrations using the non-linear dynamic pharmacokinetic (PK)ESA-EPO-R pathway model, a) Calculating the area under the curve for theESA from the resultant of step (a) as a measure for EPO receptoroccupancy of the ESA, b) Calculating the concentration of the ESA forwhich the half maximum occupancy of the EPO receptor is reached toobtain an EC50_(ESA), c) Compare the EC50_(ESA) with a predeterminedEC50_(EPOalfa) or EC50_(EPObeta), Wherein the difference between theEC50_(ES)A compared to the predetermined EC50_(EPOalfa) orEC50_(EPObeta) correlates with the difference of the biological activityof the ESA compared with the biological activity of EPO alfa or EPObeta.
 26. The method according to claim 25, wherein the EC50_(EPOalfa)or EC50_(EPObeta) are predetermined by performing in addition steps (a)to (c) with EPO alfa or EPO beta as the ESA to obtain in step (c) theEC50_(EPOalfa) or EC50_(EPObeta). 27-31. (canceled)